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/services/audio_analyzer.py

@@ -53,6 +53,7 @@ class AudioAnalyzer:
         self._running = False
         self._thread: threading.Thread | None = None
         self._lock = threading.Lock()
+        self._lifecycle_lock = threading.Lock()
         self._data: dict | None = None
         self._current_device_name: str | None = None
 
@@ -88,24 +89,26 @@ class AudioAnalyzer:
 
     def start(self) -> bool:
         """Start audio capture in a background thread. Returns False if unavailable."""
-        if self._running:
-            return True
-        if not self.available:
-            return False
+        with self._lifecycle_lock:
+            if self._running:
+                return True
+            if not self.available:
+                return False
 
-        self._running = True
-        self._thread = threading.Thread(target=self._capture_loop, daemon=True)
-        self._thread.start()
-        return True
+            self._running = True
+            self._thread = threading.Thread(target=self._capture_loop, daemon=True)
+            self._thread.start()
+            return True
 
     def stop(self) -> None:
         """Stop audio capture and cleanup."""
-        self._running = False
-        if self._thread:
-            self._thread.join(timeout=3.0)
-            self._thread = None
-        with self._lock:
-            self._data = None
+        with self._lifecycle_lock:
+            self._running = False
+            if self._thread:
+                self._thread.join(timeout=3.0)
+                self._thread = None
+            with self._lock:
+                self._data = None
 
     def get_frequency_data(self) -> dict | None:
         """Return latest frequency data (thread-safe). None if not running."""