feat: move voice enable/model config to admin UI

Replace VOICE_ENABLED env var gate with DB-backed admin setting.

- services/voice_config.py: reads voice_enabled + voice_stt_model from
  admin user's settings row (falls back to env var defaults)
- routes/admin.py: GET/PUT /api/admin/voice for admin configuration
- routes/voice.py, services/stt.py, services/tts.py: read enabled/model
  from DB via voice_config instead of Config directly
- app.py: always schedule model loaders at startup; they self-gate on
  the DB setting so no conditional needed at the call site
- SettingsView.vue: Voice section in Admin → Config tab (enable toggle +
  STT model dropdown); user Voice tab now points to admin panel when disabled

No env var required to test — enable via Settings → Admin → Config → Voice.

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

src/fabledassistant/routes/admin.py

@@ -19,6 +19,7 @@ from fabledassistant.services.backup import (
     restore_full_backup,
 )
 from fabledassistant.services.email import SMTP_SETTING_KEYS, get_base_url, get_smtp_config, is_smtp_configured, send_test_email
+from fabledassistant.services.voice_config import get_voice_config
 from fabledassistant.services.logging import get_logs, get_log_stats, log_audit
 from fabledassistant.services.notifications import send_invitation_email
 from fabledassistant.services.settings import set_setting, set_settings_batch
@@ -200,6 +201,33 @@ async def update_base_url():
     return jsonify({"status": "ok"})
 
 
+@admin_bp.route("/voice", methods=["GET"])
+@admin_required
+async def get_voice_config_route():
+    config = await get_voice_config()
+    return jsonify(config)
+
+
+@admin_bp.route("/voice", methods=["PUT"])
+@admin_required
+async def update_voice_config():
+    data = await request.get_json()
+    uid = get_current_user_id()
+    valid_models = {"tiny.en", "base.en", "small.en", "medium.en"}
+    settings: dict[str, str] = {}
+    if "voice_enabled" in data:
+        settings["voice_enabled"] = "true" if data["voice_enabled"] else "false"
+    if "voice_stt_model" in data:
+        model = str(data["voice_stt_model"])
+        if model not in valid_models:
+            return jsonify({"error": f"Invalid STT model. Choose from: {', '.join(sorted(valid_models))}"}), 400
+        settings["voice_stt_model"] = model
+    if settings:
+        await set_settings_batch(uid, settings)
+    await log_audit("voice_config", user_id=uid, username=g.user.username, ip_address=request.remote_addr, details=settings)
+    return jsonify({"status": "ok"})
+
+
 @admin_bp.route("/invitations", methods=["POST"])
 @admin_required
 async def create_invite():