Add multi-token authentication with client labels

- Replace single api_token with api_tokens dict (label: token pairs)
- Add context-aware logging to track which client made each request
- Implement token label lookup with secure comparison
- Add logging middleware to inject token labels into request context
- Update logging format to display [label] in all log messages
- Fix WebSocket authentication to use new multi-token system
- Update CLI --show-token to display all tokens with labels
- Update config generation to use api_tokens format
- Update README with multi-token documentation
- Update config.example.yaml with multiple token examples

Benefits:
- Easy identification of clients in logs (Home Assistant, mobile, web UI, etc.)
- Per-client token management and revocation
- Better security and auditability

Example log output:
2026-02-06 03:36:20,806 - [home_assistant] - WebSocket client connected

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

media_server/routes/media.py

@@ -282,10 +282,16 @@ async def websocket_endpoint(
     - {"type": "get_status"} - Request current status
     """
     # Verify token
-    if token != settings.api_token:
+    from ..auth import get_token_label, token_label_var
+
+    label = get_token_label(token) if token else None
+    if label is None:
         await websocket.close(code=4001, reason="Invalid authentication token")
         return
 
+    # Set label in context for logging
+    token_label_var.set(label)
+
     await ws_manager.connect(websocket)
 
     try: