On-demand audio visualizer capture + UI fixes

- Audio capture starts only when first client subscribes,
  stops when last client unsubscribes (saves CPU/battery)
- Add lifecycle lock to AudioAnalyzer for thread-safe start/stop
- Status badge uses local visualizer state instead of server flag
- Fix script name vertical text break on narrow screens
- Fix script grid minimum column width on small viewports

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

media_server/main.py

@@ -59,7 +59,7 @@ async def lifespan(app: FastAPI):
     await ws_manager.start_status_monitor(controller.get_status)
     logger.info("WebSocket status monitor started")
 
-    # Start audio visualizer (if enabled and dependencies available)
+    # Register audio visualizer (capture starts on-demand when clients subscribe)
     analyzer = None
     if settings.visualizer_enabled:
         from .services.audio_analyzer import get_audio_analyzer
@@ -70,11 +70,8 @@ async def lifespan(app: FastAPI):
             device_name=settings.visualizer_device,
         )
         if analyzer.available:
-            if analyzer.start():
-                await ws_manager.start_audio_monitor(analyzer)
-                logger.info("Audio visualizer started")
-            else:
-                logger.warning("Audio visualizer failed to start (no loopback device?)")
+            await ws_manager.start_audio_monitor(analyzer)
+            logger.info("Audio visualizer available (capture on-demand)")
         else:
             logger.info("Audio visualizer unavailable (install soundcard + numpy)")