feat(vision): configurability — SetupWizard ANPR toggle, footer health chip, env docs

Make the vision service genuinely configurable (was env-only).

- SetupWizard: an "ANPR" checkbox on the camera form (writes config.anpr; persisted
  only when on; sq+en) — opt-in is no longer raw JSON.
- DeviceMonitor optionally takes the VisionClient and probes /health each tick, emitting
  a "vision" pseudo-device → a Vision chip (ready/degraded/offline + recognizer) in the
  booth footer when VISION_ENABLED, no chip when off. Widened the DeviceStatus category
  union (server + web) + footer maps + devices.catVision. Verified: ready/fast_alpr when
  up, 0 chips when disabled.
- apps/vision/.env.example (Python service) + a VISION_* block in apps/server/.env.example
  (Node side) + a Configuration section in opencv-anpr-service.md covering all four
  layers and the caveats: the two processes share the VISION_ prefix but need SEPARATE
  .env files; bind /analyze to 127.0.0.1; cache model weights at deploy; an unbound anpr
  camera recognizes but every read is refused.

Build + lint green.

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

apps/server/.env.example

@@ -29,3 +29,15 @@ EVENT_SIGNING_KEY=
 # Comma-separated extra origins allowed to open the booth WebSocket (/api/ws).
 # In dev, set the Vite SPA origin. Same-origin is always allowed without this.
 WS_ALLOWED_ORIGINS=http://localhost:5173
+
+# Vision / ANPR (optional) -------------------------------------------------
+# OFF by default. The Node SERVER's view of the vision microservice (apps/vision),
+# 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".
+# 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