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.

wiki/index.md

@@ -52,6 +52,7 @@ Counts: 1 source · 14 entities · 10 concepts · 2 decision records.
 - [[device-adapter-pattern]] — business logic talks to interfaces; swap hardware → new adapter.
 - [[device-registry]] — catalog of selectable drivers per category (admin-configurable).
 - [[first-run-setup]] — admin assigns devices per lane from the catalog at install.
+- [[device-discovery]] — optional driver capability to scan the LAN (UHPPOTE UDP broadcast).
 - [[barrier-not-a-door]] — never timed-close a barrier; safety lives in barrier firmware.
 - [[trust-boundary]] — the core fork: network vs. device; auditable vs. unforgeable.
 - [[fail-state-safety]] — entry fails closed, exit fails open; manual override; watchdog.