refactor(vision): ANPR rides the entry/exit snapshot, drop polling reader

Rework the ANPR trigger to the real design: when a transient presses the button or a
subscriber passes QR/RFID, the entry/exit fires and takes its evidence snapshot — that
is the moment to recognize. snapshotAsync now takes the VisionClient and, after storing
each snapshot from an opt-in (config.anpr) camera, runs ANPR on the SAME image and
records the plate against the SAME session identity (device_events kind:"read" with
plate/confidence/region/snapshotId/source:"entry-exit-snapshot"). One image serves both
evidence and plate extraction; recognition fires only on a real entry/exit — no polling.

The entry/exit/subscription flows take an optional VisionClient and pass it through;
server.ts wires it. Removed the polling VisionReader and VISION_POLL_MS/VISION_DEDUPE_MS.

Advisory + fire-and-forget: a low-confidence/no-plate result records nothing, a vision
failure never delays or changes the open, and the plate does not feed the access
decision. Verified e2e: a simulated entry snapshot on an anpr camera (live fast_alpr)
stored the snapshot for the session and recorded {identity, plate:AA558EE, 0.999,
region:Albania, snapshotId}. Build + lint green.

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

apps/server/.env.example

@@ -35,9 +35,8 @@ WS_ALLOWED_ORIGINS=http://localhost:5173
 # which runs as a separate process with its OWN apps/vision/.env. Both sides share the
 # VISION_ prefix but are different processes — keep the two .env files separate.
 # See wiki/entities/opencv-anpr-service.md "Configuration".
+# ANPR rides the entry/exit snapshot (button / QR / RFID triggers it) — no polling.
 # VISION_ENABLED=1                       # master switch — nothing runs without it
 # VISION_URL=http://127.0.0.1:8089       # must match apps/vision VISION_HOST:VISION_PORT
 # VISION_TIMEOUT_MS=1500                 # per-request cap so a slow call can't hang the lane
-# VISION_POLL_MS=2000                    # how often each anpr camera is polled
-# VISION_DEDUPE_MS=15000                 # suppress re-firing the same plate while a car sits in frame
 # VISION_MIN_CONFIDENCE=0.5              # confidence floor; keep in sync with the service