fix(anpr): share one camera snapshot across bridge + advisory paths

On a vehicle entry, two paths captured the SAME Hikvision camera within ~1s —
the ANPR bridge (barrier-driving) and the advisory snapshotAsync (evidence/
telemetry) — each from a separate adapter instance. Hikvision serves snapshots
single-threaded, so the second concurrent GET returned HTTP 503; the bridge
then fail-softed and burned its 12s debounce, producing a ~74s "slow" subscriber
entry (observed 2026-06-25, Qazim Mulleti / AB816NN — plate read was instant at
conf 1.000; the delay was the 503/debounce churn, not recognition).

Add captureSnapshotShared() in snapshot.ts: a module-level, deviceId-keyed cache
that both paths call. It coalesces in-flight captures (the 2nd caller awaits the
1st's pull → no concurrent 503), serves a brief freshness window (1500ms) so the
bridge→advisory sequence for one vehicle reuses one frame, never caches a failure
(next caller retries), and keys by deviceId (no cross-camera/stale-vehicle reuse).
Wired into anpr-entry.ts (bridge) and snapshot.ts (advisory).

Tests: snapshot.test.ts (concurrent coalescing, TTL reuse, TTL-lapse re-pull,
failure-not-cached, per-camera keying); anpr-entry.test.ts mock updated. 168
server tests green.

NOTE: this removes the latency (the 503 collision). The separate double-entry
(two signed vehicle_entry for one car) — debounce-too-short / stamp-before-
success — is still open; less likely now but not eliminated.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/server/src/anpr-entry.test.ts

@@ -15,8 +15,13 @@ import type { SubscriptionFlow, SubscriptionMatch } from "./subscription-flow.js
 // Mock buildCamera so the bridge gets a fake camera whose captureSnapshot is a stub
 // (no registry, no network). The factory returns a fresh shot each call.
 const captureSnapshot = vi.fn(async () => ({ bytes: Buffer.from("jpg"), contentType: "image/jpeg" }));
+// The bridge now goes through captureSnapshotShared (the dedup wrapper, exercised in
+// snapshot.test.ts); here it just delegates to the fake camera's captureSnapshot so this
+// suite stays focused on the bridge's own match/debounce/emit logic.
 vi.mock("./snapshot.js", () => ({
   buildCamera: () => ({ captureSnapshot }),
+  captureSnapshotShared: (_id: string, camera: { captureSnapshot: typeof captureSnapshot }, ctx: unknown) =>
+    camera.captureSnapshot(ctx as never),
 }));
 
 // Import AFTER the mock is registered.