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.

Makefile

@@ -1,9 +1,19 @@
-BINARIES     := maglevd maglevc
+BINARIES     := maglevd maglevc maglev-frontend
 MODULE       := git.ipng.ch/ipng/vpp-maglev
 PROTO_DIR    := proto
 PROTO_FILE   := $(PROTO_DIR)/maglev.proto
 GEN_FILES    := internal/grpcapi/maglev.pb.go internal/grpcapi/maglev_grpc.pb.go
 
+# Web bundle is built by Vite and embedded by the Go binary via //go:embed.
+# Any change under cmd/frontend/web/src/ retriggers an npm build; the
+# generated cmd/frontend/web/dist/index.html is the sentinel.
+FRONTEND_WEB_SRC := $(shell find cmd/frontend/web/src -type f 2>/dev/null) \
+                    cmd/frontend/web/index.html \
+                    cmd/frontend/web/package.json \
+                    cmd/frontend/web/vite.config.ts \
+                    cmd/frontend/web/tsconfig.json
+FRONTEND_WEB_DIST := cmd/frontend/web/dist/index.html
+
 NATIVE_ARCH  := $(shell go env GOARCH)
 VERSION      := 0.1.1
 COMMIT_HASH  := $(shell git rev-parse --short HEAD 2>/dev/null || echo unknown)
@@ -16,24 +26,35 @@ TEST ?= tests/
 
 VPP_API_DIR ?= $(HOME)/src/vpp/build-root/install-vpp_debug-native/vpp/share/vpp/api
 
-.PHONY: all build build-amd64 build-arm64 test proto vpp-binapi lint fixstyle pkg-deb robot-test clean
+.PHONY: all build build-amd64 build-arm64 test proto vpp-binapi lint fixstyle fixstyle-web pkg-deb robot-test clean maglev-frontend-web
 
 all: build
 
-build: $(GEN_FILES)
+build: $(GEN_FILES) $(FRONTEND_WEB_DIST)
 	mkdir -p build/$(NATIVE_ARCH)
 	go build -ldflags "$(LDFLAGS)" -o build/$(NATIVE_ARCH)/maglevd ./cmd/maglevd/
 	go build -ldflags "$(LDFLAGS)" -o build/$(NATIVE_ARCH)/maglevc ./cmd/maglevc/
+	go build -ldflags "$(LDFLAGS)" -o build/$(NATIVE_ARCH)/maglev-frontend ./cmd/frontend/
 
-build-amd64: $(GEN_FILES)
+build-amd64: $(GEN_FILES) $(FRONTEND_WEB_DIST)
 	mkdir -p build/amd64
 	GOOS=linux GOARCH=amd64 go build -ldflags "$(LDFLAGS)" -o build/amd64/maglevd ./cmd/maglevd/
 	GOOS=linux GOARCH=amd64 go build -ldflags "$(LDFLAGS)" -o build/amd64/maglevc ./cmd/maglevc/
+	GOOS=linux GOARCH=amd64 go build -ldflags "$(LDFLAGS)" -o build/amd64/maglev-frontend ./cmd/frontend/
 
-build-arm64: $(GEN_FILES)
+build-arm64: $(GEN_FILES) $(FRONTEND_WEB_DIST)
 	mkdir -p build/arm64
 	GOOS=linux GOARCH=arm64 go build -ldflags "$(LDFLAGS)" -o build/arm64/maglevd ./cmd/maglevd/
 	GOOS=linux GOARCH=arm64 go build -ldflags "$(LDFLAGS)" -o build/arm64/maglevc ./cmd/maglevc/
+	GOOS=linux GOARCH=arm64 go build -ldflags "$(LDFLAGS)" -o build/arm64/maglev-frontend ./cmd/frontend/
+
+# maglev-frontend-web rebuilds the SolidJS bundle. The Go binary embeds the
+# resulting cmd/frontend/web/dist/ via //go:embed, so a `go build` after
+# this target picks up any asset changes automatically.
+maglev-frontend-web: $(FRONTEND_WEB_DIST)
+
+$(FRONTEND_WEB_DIST): $(FRONTEND_WEB_SRC)
+	cd cmd/frontend/web && npm install && npm run build
 
 pkg-deb: build-amd64 build-arm64
 	debian/build-deb.sh amd64 $(VERSION) $(COMMIT_HASH)
@@ -71,9 +92,12 @@ vpp-binapi:
 		lb lb_types
 	rm -f internal/vpp/binapi/lb/lb_rpc.ba.go
 
-fixstyle:
+fixstyle: fixstyle-web
 	gofmt -w .
 
+fixstyle-web:
+	cd cmd/frontend/web && npx prettier --write .
+
 lint:
 	golangci-lint run ./...