feat(qbzd): integrate daemon discovery into CastPicker

QBZ Daemon tab appears first in the device picker alongside
Chromecast and DLNA. Discovered daemons show name + host:port.

Clicking a daemon:
1. Pings to verify it's reachable
2. Connects via playbackTargetStore
3. Starts SSE event subscription
4. Closes picker

Connected daemon shows in the connected banner with disconnect.
Disconnecting returns to local playback mode.

i18n: noQbzdFound + noQbzdFoundHint in all 5 locales.

cc

src/lib/i18n/locales/de.json

@@ -563,6 +563,8 @@
   "player": {
     "nowPlaying": "Aktuell abgespielt",
     "controllingRemote": "Steuert: {name}",
+    "noQbzdFound": "Keine QBZ-Daemons in Ihrem Netzwerk gefunden",
+    "noQbzdFoundHint": "Stellen Sie sicher, dass qbzd auf dem Zielgerat lauft",
     "queue": "Warteschlange",
     "upNext": "Als Nächstes",
     "ofTotal": "von",