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/device-events.ts

@@ -1,5 +1,6 @@
 import { EventEmitter } from "node:events";
 import type { PrinterStatus } from "@parking/devices";
+import type { LedgerEventRow } from "@parking/db";
 
 // Internal event bus for device-originated events (button presses, etc.).
 // Hardware drivers / inbound device pushes emit here; business logic (entry
@@ -74,6 +75,21 @@ class DeviceEventBus extends EventEmitter {
     this.on("printer-status", cb);
     return () => this.off("printer-status", cb);
   }
+
+  /**
+   * Emitted AFTER a signed business event is appended to the ledger (entry, exit,
+   * payment, void, …). The payload is the persisted row — business facts only, no
+   * secrets — so it is safe to fan out to authenticated booth clients over the WS.
+   * This is a read-side notification ONLY: it never feeds back into append/sign/
+   * chain logic. See event-log.ts (emitted from EventLog.append) and routes/ws.ts.
+   */
+  emitLedger(event: LedgerEventRow): void {
+    this.emit("ledger", event);
+  }
+  onLedger(cb: (event: LedgerEventRow) => void): () => void {
+    this.on("ledger", cb);
+    return () => this.off("ledger", cb);
+  }
 }
 
 /** Process-wide device event bus. */