Fix SDR device lock-up from unreleased device registry on process crash

Stream threads for sensor, pager, acars, rtlamr, dmr, and dsc modes
never called release_sdr_device() when their SDR process crashed,
leaving devices permanently locked in the registry. Also fixes orphaned
companion processes (rtl_fm, rtl_tcp) not being killed on crash, start
path failures leaking processes, DMR stop handler missing lock, and
listening post/audio websocket pkill nuking all system-wide rtl_fm
processes. Wires up register_process()/unregister_process() so the
atexit/signal cleanup safety net actually works, and adds rtl_tcp,
rtl_power, rtlamr, ffmpeg to the killall endpoint.

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

routes/sensor.py

@@ -19,7 +19,7 @@ from utils.validation import (
     validate_rtl_tcp_host, validate_rtl_tcp_port
 )
 from utils.sse import format_sse
-from utils.process import safe_terminate, register_process
+from utils.process import safe_terminate, register_process, unregister_process
 from utils.sdr import SDRFactory, SDRType
 
 sensor_bp = Blueprint('sensor', __name__)
@@ -59,10 +59,24 @@ def stream_sensor_output(process: subprocess.Popen[bytes]) -> None:
     except Exception as e:
         app_module.sensor_queue.put({'type': 'error', 'text': str(e)})
     finally:
-        process.wait()
+        global sensor_active_device
+        # Ensure process is terminated
+        try:
+            process.terminate()
+            process.wait(timeout=2)
+        except Exception:
+            try:
+                process.kill()
+            except Exception:
+                pass
+        unregister_process(process)
         app_module.sensor_queue.put({'type': 'status', 'text': 'stopped'})
         with app_module.sensor_lock:
             app_module.sensor_process = None
+        # Release SDR device
+        if sensor_active_device is not None:
+            app_module.release_sdr_device(sensor_active_device)
+            sensor_active_device = None
 
 
 @sensor_bp.route('/start_sensor', methods=['POST'])
@@ -149,6 +163,7 @@ def start_sensor() -> Response:
                 stdout=subprocess.PIPE,
                 stderr=subprocess.PIPE
             )
+            register_process(app_module.sensor_process)
 
             # Start output thread
             thread = threading.Thread(target=stream_sensor_output, args=(app_module.sensor_process,))