New maglev-frontend component; promote LB sync events to INFO

Introduces maglev-frontend, a responsive, real-time web dashboard for one
or more running maglevd instances. Source lives at cmd/frontend/; the
built binary is maglev-frontend. It is a single Go process with the
SolidJS SPA embedded via //go:embed — no runtime file dependencies.

Architecture
 - One persistent gRPC connection per configured maglevd (-server A,B,C).
   Each connection runs three background loops: a WatchEvents stream
   subscribed at log_level=debug for live events, a 30s refresh loop as
   a safety net for drift, and a 5s health loop that surfaces connection
   drops quickly.
 - In-process pub/sub broker with a 30s / 2000-event replay ring using
   <epoch>-<seq> monotonic IDs. Short browser reconnects (nginx idle,
   wifi flap, laptop wake) silently replay buffered events via the
   EventSource Last-Event-ID header; longer outages or frontend restarts
   fall through to a "resync" event that triggers a full state refetch.
 - HTTP surface: /view/ (SPA), /view/api/state, /view/api/state/{name},
   /view/api/maglevds, /view/api/version, /view/api/events (SSE),
   /healthz, and an /admin/* placeholder returning 501 for a future
   basic-auth mutation surface.
 - SSE handler follows the full operational checklist: retry hint, 15s
   : ping heartbeat, Flush after every write, r.Context().Done() teardown,
   X-Accel-Buffering: no, and no gzip.

SolidJS SPA (cmd/frontend/web/, Vite + TypeScript)
 - solid-js/store for a reactive per-maglevd state tree; reducers apply
   backend transitions, maglevd-status flips, and resync refetches.
 - Scope selector tabs for multi-maglevd support, per-maglevd frontend
   cards with pool tables showing state, configured weight, effective
   weight, and last-transition age.
 - ProbeHeartbeat component turns a middle-dot into ❤️ on probe-start and
   back on probe-done, driven by real log events; fixed-size wrapper so
   the emoji swap doesn't jiggle the row.
 - Flash wrapper animates any primitive on change (1s yellow fade via
   Web Animations API, skipped on first mount). Wired into the state
   badge, configured weight, and effective weight columns.
 - DebugPanel: chronological rolling event tail with tail-style auto-
   scroll, pause/resume, and scope/firehose filter. Syntactic highlight
   for vpp-lb-sync-* events with fixed-order attribute formatting.
 - Live effective_weight updates: vpp-lb-sync-as-added/removed/weight-
   updated log events are routed through a reducer that walks the
   snapshot's pool rows and sets effective_weight on every match
   without waiting for the 30s refresh.
 - Header shows build version + commit with build date in a tooltip,
   fetched once from /view/api/version on mount.
 - Prettier wired in as the web-side fixstyle; make fixstyle now tidies
   both Go and web in one shot via a new fixstyle-web target.

Per-mutation VPP LB sync logging
 - Promotes the addVIP/delVIP/addAS/delAS/setASWeight helpers from
   slog.Debug to slog.Info and renames them from vpp-lbsync-* to
   vpp-lb-sync-{vip-added,vip-removed,as-added,as-removed,as-weight-
   updated}. Matching rename for vpp-lb-sync-start / -done / -error /
   -vip-recreate. The Prometheus metric name (maglev_vpp_lbsync_total)
   is left alone to preserve dashboards.
 - setASWeight now takes the prior weight so the event can emit
   from=X to=Y and the UI can show the delta.
 - The vip field in every event is the bare address (no /32 or /128
   mask), matching the CLI output style.
 - Any listener on the gRPC WatchEvents stream — CLI watch events or
   maglev-frontend — now sees every VIP/AS dataplane change in real
   time without needing to raise the log level.

Build and tooling
 - Makefile: maglev-frontend added to BINARIES; build / build-amd64 /
   build-arm64 emit the binary alongside maglevd and maglevc. A new
   maglev-frontend-web target rebuilds the SolidJS bundle via npm.
 - web/dist/ is tracked so a bare `go build` keeps working for Go-only
   contributors and CI.
 - .gitignore skips cmd/frontend/web/node_modules/.

Stability fixes
 - maglevd's WatchEvents synthetic replay events (from==to, at_unix_ns=0)
   were corrupting the frontend's LastTransition cache with at=0,
   rendering as "20555d ago" in the browser. Client now skips synthetic
   events: the cache comes from refreshAll and doesn't need them.
 - Frontends, Backends, and HealthChecks are now served in the order
   returned by the corresponding List* RPC instead of Go map iteration
   order, so reloads and refreshes keep the SPA stable.

internal/vpp/client.go

@@ -205,7 +205,7 @@ func (c *Client) lbSyncLoop(ctx context.Context) {
 		}
 
 		if err := c.SyncLBStateAll(cfg); err != nil {
-			slog.Warn("vpp-lbsync-error", "err", err)
+			slog.Warn("vpp-lb-sync-error", "err", err)
 		}
 		next = time.Now().Add(interval)
 	}

internal/vpp/lbsync.go

@@ -108,7 +108,7 @@ func (c *Client) SyncLBStateAll(cfg *config.Config) error {
 	}
 	defer ch.Close()
 
-	slog.Info("vpp-lbsync-start",
+	slog.Info("vpp-lb-sync-start",
 		"scope", "all",
 		"vips-desired", len(desired),
 		"vips-current", len(cur.VIPs))
@@ -150,7 +150,7 @@ func (c *Client) SyncLBStateAll(cfg *config.Config) error {
 	}
 
 	recordSyncStats("all", &st)
-	slog.Info("vpp-lbsync-done",
+	slog.Info("vpp-lb-sync-done",
 		"scope", "all",
 		"vip-added", st.vipAdd,
 		"vip-removed", st.vipDel,
@@ -190,10 +190,10 @@ func (c *Client) SyncLBStateVIP(cfg *config.Config, feName string) error {
 	}
 	defer ch.Close()
 
-	slog.Info("vpp-lbsync-start",
+	slog.Info("vpp-lb-sync-start",
 		"scope", "vip",
 		"frontend", feName,
-		"prefix", d.Prefix.String(),
+		"vip", d.Prefix.IP.String(),
 		"protocol", protocolName(d.Protocol),
 		"port", d.Port)
 
@@ -207,7 +207,7 @@ func (c *Client) SyncLBStateVIP(cfg *config.Config, feName string) error {
 		return err
 	}
 	recordSyncStats("vip", &st)
-	slog.Info("vpp-lbsync-done",
+	slog.Info("vpp-lb-sync-done",
 		"scope", "vip",
 		"frontend", feName,
 		"vip-added", st.vipAdd,
@@ -243,8 +243,8 @@ func reconcileVIP(ch *loggedChannel, d desiredVIP, cur *LBVIP, curSticky bool, s
 	}
 
 	if curSticky != d.SrcIPSticky {
-		slog.Info("vpp-lbsync-vip-recreate",
-			"prefix", d.Prefix.String(),
+		slog.Info("vpp-lb-sync-vip-recreate",
+			"vip", d.Prefix.IP.String(),
 			"protocol", protocolName(d.Protocol),
 			"port", d.Port,
 			"reason", "src-ip-sticky-changed",
@@ -277,7 +277,7 @@ func reconcileVIP(ch *loggedChannel, d desiredVIP, cur *LBVIP, curSticky bool, s
 		if _, keep := d.ASes[addr]; keep {
 			continue
 		}
-		if err := delAS(ch, cur.Prefix, cur.Protocol, cur.Port, a.Address); err != nil {
+		if err := delAS(ch, cur.Prefix, cur.Protocol, cur.Port, a.Address, a.Weight); err != nil {
 			return err
 		}
 		st.asDel++
@@ -299,7 +299,7 @@ func reconcileVIP(ch *loggedChannel, d desiredVIP, cur *LBVIP, curSticky bool, s
 			// (i.e. the backend was disabled, not merely drained). Steady-
 			// state syncs where weight doesn't change never re-flush.
 			flush := a.Flush && c.Weight > 0 && a.Weight == 0
-			if err := setASWeight(ch, d.Prefix, d.Protocol, d.Port, a, flush); err != nil {
+			if err := setASWeight(ch, d.Prefix, d.Protocol, d.Port, a, c.Weight, flush); err != nil {
 				return err
 			}
 			st.asWeight++
@@ -311,7 +311,7 @@ func reconcileVIP(ch *loggedChannel, d desiredVIP, cur *LBVIP, curSticky bool, s
 // removeVIP flushes all ASes from a VIP and then deletes the VIP itself.
 func removeVIP(ch *loggedChannel, v LBVIP, st *syncStats) error {
 	for _, as := range v.ASes {
-		if err := delAS(ch, v.Prefix, v.Protocol, v.Port, as.Address); err != nil {
+		if err := delAS(ch, v.Prefix, v.Protocol, v.Port, as.Address, as.Weight); err != nil {
 			return err
 		}
 		st.asDel++
@@ -441,8 +441,8 @@ func addVIP(ch *loggedChannel, d desiredVIP) error {
 	if reply.Retval != 0 {
 		return fmt.Errorf("lb_add_del_vip_v2 add %s: retval=%d", d.Prefix, reply.Retval)
 	}
-	slog.Debug("vpp-lbsync-vip-add",
-		"prefix", d.Prefix.String(),
+	slog.Info("vpp-lb-sync-vip-added",
+		"vip", d.Prefix.IP.String(),
 		"protocol", protocolName(d.Protocol),
 		"port", d.Port,
 		"encap", encapName(encap),
@@ -464,8 +464,8 @@ func delVIP(ch *loggedChannel, prefix *net.IPNet, protocol uint8, port uint16) e
 	if reply.Retval != 0 {
 		return fmt.Errorf("lb_add_del_vip_v2 del %s: retval=%d", prefix, reply.Retval)
 	}
-	slog.Debug("vpp-lbsync-vip-del",
-		"prefix", prefix.String(),
+	slog.Info("vpp-lb-sync-vip-removed",
+		"vip", prefix.IP.String(),
 		"protocol", protocolName(protocol),
 		"port", port)
 	return nil
@@ -487,8 +487,8 @@ func addAS(ch *loggedChannel, prefix *net.IPNet, protocol uint8, port uint16, a
 	if reply.Retval != 0 {
 		return fmt.Errorf("lb_add_del_as_v2 add %s@%s: retval=%d", a.Address, prefix, reply.Retval)
 	}
-	slog.Debug("vpp-lbsync-as-add",
-		"vip", prefix.String(),
+	slog.Info("vpp-lb-sync-as-added",
+		"vip", prefix.IP.String(),
 		"protocol", protocolName(protocol),
 		"port", port,
 		"address", a.Address.String(),
@@ -496,7 +496,7 @@ func addAS(ch *loggedChannel, prefix *net.IPNet, protocol uint8, port uint16, a
 	return nil
 }
 
-func delAS(ch *loggedChannel, prefix *net.IPNet, protocol uint8, port uint16, addr net.IP) error {
+func delAS(ch *loggedChannel, prefix *net.IPNet, protocol uint8, port uint16, addr net.IP, fromWeight uint8) error {
 	req := &lb.LbAddDelAsV2{
 		Pfx:       ip_types.NewAddressWithPrefix(*prefix),
 		Protocol:  protocol,
@@ -512,15 +512,16 @@ func delAS(ch *loggedChannel, prefix *net.IPNet, protocol uint8, port uint16, ad
 	if reply.Retval != 0 {
 		return fmt.Errorf("lb_add_del_as_v2 del %s@%s: retval=%d", addr, prefix, reply.Retval)
 	}
-	slog.Debug("vpp-lbsync-as-del",
-		"vip", prefix.String(),
+	slog.Info("vpp-lb-sync-as-removed",
+		"vip", prefix.IP.String(),
 		"protocol", protocolName(protocol),
 		"port", port,
-		"address", addr.String())
+		"address", addr.String(),
+		"weight", fromWeight)
 	return nil
 }
 
-func setASWeight(ch *loggedChannel, prefix *net.IPNet, protocol uint8, port uint16, a desiredAS, flush bool) error {
+func setASWeight(ch *loggedChannel, prefix *net.IPNet, protocol uint8, port uint16, a desiredAS, fromWeight uint8, flush bool) error {
 	req := &lb.LbAsSetWeight{
 		Pfx:       ip_types.NewAddressWithPrefix(*prefix),
 		Protocol:  protocol,
@@ -536,12 +537,13 @@ func setASWeight(ch *loggedChannel, prefix *net.IPNet, protocol uint8, port uint
 	if reply.Retval != 0 {
 		return fmt.Errorf("lb_as_set_weight %s@%s: retval=%d", a.Address, prefix, reply.Retval)
 	}
-	slog.Debug("vpp-lbsync-as-weight",
-		"vip", prefix.String(),
+	slog.Info("vpp-lb-sync-as-weight-updated",
+		"vip", prefix.IP.String(),
 		"protocol", protocolName(protocol),
 		"port", port,
 		"address", a.Address.String(),
-		"weight", a.Weight,
+		"from", fromWeight,
+		"to", a.Weight,
 		"flush", flush)
 	return nil
 }