Fix SSE first-byte delay in ADS-B and controller streams; harden WebSocket init

- Add immediate keepalive to /adsb/stream generator so the Werkzeug dev
  server flushes response headers immediately on tracking start, preventing
  the 30-second delay before the aircraft map begins receiving data
- Same fix for /controller/stream/all used by the ADSB dashboard in agent mode
- Widen WebSocket init exception guards in app.py from ImportError to
  Exception so any startup failure (e.g. RuntimeError from flask-sock on
  an unsupported WSGI server) is caught instead of propagating

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

app.py

@@ -1128,35 +1128,35 @@ def _init_app() -> None:
     try:
         from routes.audio_websocket import init_audio_websocket
         init_audio_websocket(app)
-    except ImportError:
+    except Exception:
         pass
 
     # Initialize KiwiSDR WebSocket audio proxy
     try:
         from routes.websdr import init_websdr_audio
         init_websdr_audio(app)
-    except ImportError:
+    except Exception:
         pass
 
     # Initialize WebSocket for waterfall streaming
     try:
         from routes.waterfall_websocket import init_waterfall_websocket
         init_waterfall_websocket(app)
-    except ImportError:
+    except Exception:
         pass
 
     # Initialize WebSocket for meteor scatter monitoring
     try:
         from routes.meteor_websocket import init_meteor_websocket
         init_meteor_websocket(app)
-    except ImportError:
+    except Exception:
         pass
 
     # Initialize WebSocket for ground station live waterfall
     try:
         from routes.ground_station import init_ground_station_websocket
         init_ground_station_websocket(app)
-    except ImportError:
+    except Exception:
         pass
 
     # Defer heavy/network operations so the worker can serve requests immediately

routes/adsb.py

@@ -1167,6 +1167,9 @@ def stream_adsb():
 
     def generate():
         last_keepalive = time.time()
+        # Send immediate keepalive so Werkzeug dev server flushes response
+        # headers right away (it buffers until first body byte is written).
+        yield format_sse({'type': 'keepalive'})
 
         try:
             while True:

routes/controller.py

@@ -673,6 +673,7 @@ def stream_all_agents():
     def generate() -> Generator[str, None, None]:
         last_keepalive = time.time()
         keepalive_interval = 30.0
+        yield format_sse({'type': 'keepalive'})
 
         try:
             while True: