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.

cmd/frontend/web/src/views/FrontendCard.tsx

@@ -0,0 +1,66 @@
+import { For, type Component } from "solid-js";
+import type { FrontendSnapshot, StateSnapshot } from "../types";
+import BackendRow from "./BackendRow";
+
+type Props = {
+  snap: StateSnapshot;
+  frontend: FrontendSnapshot;
+};
+
+const FrontendCard: Component<Props> = (props) => {
+  const backendByName = () => Object.fromEntries(props.snap.backends.map((b) => [b.name, b]));
+  const fe = () => props.frontend;
+
+  return (
+    <section class="frontend-card">
+      <header class="frontend-header">
+        <h2>{fe().name}</h2>
+        <div class="frontend-meta">
+          <span class="addr">
+            {fe().address}:{fe().port}
+          </span>
+          <span class="proto">{fe().protocol.toUpperCase()}</span>
+          {fe().src_ip_sticky && <span class="tag">sticky</span>}
+        </div>
+        {fe().description && <p class="frontend-desc">{fe().description}</p>}
+      </header>
+
+      <For each={fe().pools}>
+        {(pool) => (
+          <div class="pool-block">
+            <h3 class="pool-name">pool: {pool.name}</h3>
+            <table class="backend-table">
+              <thead>
+                <tr>
+                  <th>backend</th>
+                  <th>address</th>
+                  <th>state</th>
+                  <th class="numeric">weight</th>
+                  <th class="numeric">effective</th>
+                  <th>last transition</th>
+                </tr>
+              </thead>
+              <tbody>
+                <For each={pool.backends}>
+                  {(pb) => {
+                    const backend = backendByName()[pb.name];
+                    if (!backend) return null;
+                    return (
+                      <BackendRow
+                        maglevd={props.snap.maglevd.name}
+                        backend={backend}
+                        poolBackend={pb}
+                      />
+                    );
+                  }}
+                </For>
+              </tbody>
+            </table>
+          </div>
+        )}
+      </For>
+    </section>
+  );
+};
+
+export default FrontendCard;