Fix TSCM sweep scan resilience and add per-device error isolation

The sweep loop's WiFi/BT/RF scan processing had unprotected
timeline_manager.add_observation() calls that could crash an entire
scan iteration, silently preventing all device events from reaching
the frontend. Additionally, scan interval timestamps were only updated
at the end of processing, causing tight retry loops on persistent errors.

- Wrap timeline observation calls in try/except for all three protocols
- Move last_*_scan timestamp updates immediately after scan completes
- Add per-device try/except so one bad device doesn't block others
- Emit sweep_progress after WiFi scan for real-time status visibility
- Log warning when WiFi scan returns 0 networks for easier diagnosis
- Add known_device and score_modifier fields to correlation engine
- Add TSCM scheduling, cases, known devices, and advanced WiFi indicators

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

utils/sstv.py

@@ -245,10 +245,11 @@ class SSTVDecoder:
         # Doppler tracking
         self._doppler_tracker = DopplerTracker('ISS')
         self._doppler_enabled = False
-        self._last_doppler_info: DopplerInfo | None = None
-
-        # Ensure output directory exists
-        self._output_dir.mkdir(parents=True, exist_ok=True)
+        self._last_doppler_info: DopplerInfo | None = None
+        self._file_decoder: str | None = None
+
+        # Ensure output directory exists
+        self._output_dir.mkdir(parents=True, exist_ok=True)
 
         # Detect available decoder
         self._decoder = self._detect_decoder()
@@ -265,21 +266,23 @@ class SSTVDecoder:
     def _detect_decoder(self) -> str | None:
         """Detect which SSTV decoder is available."""
         # Check for slowrx (command-line SSTV decoder)
-        try:
-            result = subprocess.run(['which', 'slowrx'], capture_output=True, timeout=5)
-            if result.returncode == 0:
-                return 'slowrx'
-        except Exception:
-            pass
+        try:
+            result = subprocess.run(['which', 'slowrx'], capture_output=True, timeout=5)
+            if result.returncode == 0:
+                self._file_decoder = 'slowrx'
+                return 'slowrx'
+        except Exception:
+            pass
 
         # Note: qsstv is GUI-only and not suitable for headless/server operation
 
-        # Check for Python sstv package
-        try:
-            import sstv
-            return 'python-sstv'
-        except ImportError:
-            pass
+        # Check for Python sstv package
+        try:
+            import sstv
+            self._file_decoder = 'python-sstv'
+            return None
+        except ImportError:
+            pass
 
         logger.warning("No SSTV decoder found. Install slowrx (apt install slowrx) or python sstv package. Note: qsstv is GUI-only and not supported for headless operation.")
         return None
@@ -691,11 +694,13 @@ class SSTVDecoder:
         if not audio_path.exists():
             raise FileNotFoundError(f"Audio file not found: {audio_path}")
 
-        images = []
-
-        if self._decoder == 'slowrx':
-            # Use slowrx with file input
-            output_file = self._output_dir / f"sstv_{datetime.now().strftime('%Y%m%d_%H%M%S')}.png"
+        images = []
+
+        decoder = self._decoder or self._file_decoder
+
+        if decoder == 'slowrx':
+            # Use slowrx with file input
+            output_file = self._output_dir / f"sstv_{datetime.now().strftime('%Y%m%d_%H%M%S')}.png"
 
             cmd = ['slowrx', '-o', str(self._output_dir), str(audio_path)]
             result = subprocess.run(cmd, capture_output=True, timeout=300)
@@ -715,10 +720,10 @@ class SSTVDecoder:
                         )
                         images.append(image)
 
-        elif self._decoder == 'python-sstv':
-            # Use Python sstv library
-            try:
-                from sstv.decode import SSTVDecoder as PythonSSTVDecoder
+        elif decoder == 'python-sstv':
+            # Use Python sstv library
+            try:
+                from sstv.decode import SSTVDecoder as PythonSSTVDecoder
                 from PIL import Image
 
                 decoder = PythonSSTVDecoder(str(audio_path))