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/src/exit-flow.ts

@@ -2,6 +2,7 @@ import { desc, eq, ledgerEvents, sessions, tariffVersions, tariffs, type Db, typ
 import { registry, type AccessControlDevice } from "@parking/devices";
 import { firstRelayByDirection, type ResolvedRelay } from "./device-resolve.js";
 import { snapshotAsync } from "./snapshot.js";
+import type { VisionClient } from "./vision-client.js";
 import { computeFee, reasonPayload, renderReasonEn, type LedgerPayload, type TariffStructure } from "@parking/shared";
 import type { FastifyBaseLogger } from "fastify";
 import type { DeviceReadEvent, ReadOutcome } from "./device-events.js";
@@ -61,11 +62,14 @@ export class ExitFlow {
   readonly #log: EventLog;
   readonly #logger: FastifyBaseLogger;
   readonly #inFlight = new Set<string>();
+  /** Optional vision client — passed to snapshotAsync so ANPR runs on the exit image. */
+  readonly #vision: VisionClient | null;
 
-  constructor(db: Db, log: EventLog, logger: FastifyBaseLogger) {
+  constructor(db: Db, log: EventLog, logger: FastifyBaseLogger, vision: VisionClient | null = null) {
     this.#db = db;
     this.#log = log;
     this.#logger = logger;
+    this.#vision = vision;
   }
 
   /**
@@ -364,6 +368,7 @@ export class ExitFlow {
       direction: "exit",
       identity,
       logger: this.#logger,
+      vision: this.#vision,
     }).catch((err) => this.#logger.error(`exit snapshot error: ${(err as Error).message}`));
   }