feat: show recognized plate in live feed + active sessions

Surface the advisory ANPR plate (device_events kind="read", keyed by
session identity — unsigned, prunable, never an access decision) next to
entry/exit events in the live feed and on active-session rows.

Resolved at serialize time (new plate-lookup.ts; prefers an entry read;
one device_events scan per page) like subscriber-name enrichment — the
signed ledger is untouched. Adds plate? to the shared LedgerEvent and to
ActiveSession/SessionLookup; a small amber badge in the UI.

Caveat: a vehicle_entry is signed + pushed over WS before the async ANPR
read lands, so a fresh feed row may show no plate until reload; always
present on active sessions.

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

apps/web/src/api.ts

@@ -762,6 +762,8 @@ export interface SessionLookup {
   subscription: boolean;
   subscriptionId: string | null;
   subscriptionHolder: string | null;
+  /** Advisory licence plate recognized for this session (ANPR). Null when none. */
+  plate: string | null;
 }
 
 /** Look up a ticket/session for the booth modal (entry/exit, paid, amount owed). */
@@ -789,6 +791,8 @@ export interface ActiveSession {
   subscription: boolean;
   subscriptionId: string | null;
   subscriptionHolder: string | null;
+  /** Advisory licence plate recognized for this session (ANPR). Null when none. */
+  plate: string | null;
 }
 
 /** Active sessions: still-inside OR exited-but-within-grace (barrier unconfirmed). */