feat: hot-reload voice models without server restart

Voice enabled/STT model are now DB-backed (admin settings), not env
vars. Added reload_stt_model()/reload_tts_model() that clear singletons
under lock and re-trigger loading. POST /api/admin/voice/reload triggers
both in background tasks. Settings UI polls /api/voice/status every 2.5s
until models are ready, with spinner feedback.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/fabledassistant/routes/admin.py

@@ -228,6 +228,17 @@ async def update_voice_config():
     return jsonify({"status": "ok"})
 
 
+@admin_bp.route("/voice/reload", methods=["POST"])
+@admin_required
+async def reload_voice_models():
+    """Reload STT and TTS models in the background without a server restart."""
+    from fabledassistant.services.stt import reload_stt_model
+    from fabledassistant.services.tts import reload_tts_model
+    asyncio.create_task(reload_stt_model())
+    asyncio.create_task(reload_tts_model())
+    return jsonify({"status": "loading"})
+
+
 @admin_bp.route("/invitations", methods=["POST"])
 @admin_required
 async def create_invite():