feat(server): live booth WebSocket feed (/api/ws)

Add @fastify/websocket. EventLog fires an onAppended callback after each durable
append; device-events gains a ledger channel (emitLedger). /api/ws fans out
ledger + occupancy + printer-status to authenticated booth clients. Origin
allowlist (WS_ALLOWED_ORIGINS) replaces CSRF for the handshake (anti-CSWSH).

Note: server.ts also reflects later booth route wiring; the final HEAD builds.

apps/server/src/event-log.ts

@@ -92,13 +92,23 @@ export class EventLog {
    *  (JWT-fallback → dedicated key → ATECC608). Defaults to the append signer for
    *  callers that don't pass one (single-key chains, tests). */
   readonly #resolveVerifier: SignerResolver;
+  /** Optional read-side notification, fired AFTER a row is durably inserted. Used
+   *  to fan the event out to live booth clients (WS). It is best-effort and must
+   *  NOT influence the append/sign/chain path — a throwing/absent sink is ignored. */
+  readonly #onAppended?: (row: LedgerEventRow) => void;
   /** Serialize appends: each waits for the previous to finish. */
   #tail: Promise<unknown> = Promise.resolve();
 
-  constructor(db: Db, signer: Signer, resolveVerifier?: SignerResolver) {
+  constructor(
+    db: Db,
+    signer: Signer,
+    resolveVerifier?: SignerResolver,
+    onAppended?: (row: LedgerEventRow) => void,
+  ) {
     this.#db = db;
     this.#signer = signer;
     this.#resolveVerifier = resolveVerifier ?? (() => signer);
+    this.#onAppended = onAppended;
   }
 
   /** Append one event to the chain. Returns the persisted row. Serialized. */
@@ -106,7 +116,16 @@ export class EventLog {
     const run = this.#tail.then(() => this.#appendNow(input));
     // Keep the chain going even if one append rejects (don't wedge the lock).
     this.#tail = run.catch(() => undefined);
-    return run;
+    // Read-side notification, AFTER the row is durably written. Wrapped so a
+    // failing sink can never reject the append or break the chain lock above.
+    return run.then((row) => {
+      try {
+        this.#onAppended?.(row);
+      } catch {
+        // best-effort fan-out only — swallow.
+      }
+      return row;
+    });
   }
 
   #appendNow(input: AppendInput): LedgerEventRow {