Add device discovery (UHPPOTE LAN scan) to setup

UHPPOTE controllers self-announce via UDP broadcast, but the frontend had no way
to find them — the admin had to type the serial blind. Add a generic discovery
capability and surface it in the setup wizard.

packages/devices:
- DiscoverableDriver capability + DiscoveredDevice type + isDiscoverable() guard
  on the registry (optional, so any driver can opt in).
- uhppote driver implements discover() via uhppoted getDevices (UDP broadcast),
  mapping each controller's serial/IP/firmware into a DiscoveredDevice; extract
  shared buildCtx().

apps/server:
- GET /api/setup/discover/:driverId (admin-only): runs discover() and
  health-checks each found device so reachability shows before assigning.
- catalog now returns a `discoverable` driver-id list.

apps/web:
- SetupWizard "Scan for controllers" button for discoverable drivers; lists found
  devices with health badges; selecting one auto-fills serial + host. api client
  gains discoverDevices().

wiki: new device-discovery concept; cross-link from registry/setup/uhppote;
note the broadcast-permission (EACCES) deployment caveat; index + log.

Verified: catalog flags uhppote discoverable; discover runs and fails gracefully
without hardware; non-discoverable driver -> 400; missing token -> 401.

packages/devices/src/drivers/uhppoted.d.ts

@@ -24,6 +24,22 @@ declare module "uhppoted" {
     locale?: string;
   }
 
+  export interface DiscoveredController {
+    deviceId: number;
+    device: {
+      serialNumber: number;
+      address: string;
+      netmask: string;
+      gateway: string;
+      MAC: string;
+      version: string;
+      date: string;
+    };
+  }
+
+  /** UDP broadcast discovery — returns every controller answering on the LAN. */
+  export function getDevices(ctx: Ctx): Promise<DiscoveredController[]>;
+
   export function openDoor(
     ctx: Ctx,
     controller: Controller,
@@ -56,6 +72,7 @@ declare module "uhppoted" {
   // CommonJS default export (module.exports = { ... }). Destructure from this.
   const uhppoted: {
     Config: typeof Config;
+    getDevices: typeof getDevices;
     openDoor: typeof openDoor;
     getStatus: typeof getStatus;
     getEvent: typeof getEvent;