feat(api): add sdr_claims to /health and surface /devices/status

/health now includes sdr_claims: a dict mapping 'sdr_type:device_index'
to the mode currently using that device (e.g. {"rtlsdr:0": "pager"}).
Empty when no devices are in use.

/devices/status already existed and returns the full device list with
in_use/used_by per device — documented in the issue response.

Closes #158

app.py

@@ -478,15 +478,15 @@ def login():
 
     return render_template('login.html', version=VERSION)
 
-@app.route('/')
-def index() -> str:
-    if request.args.get('mode') == 'satellite':
-        return redirect(url_for('satellite.satellite_dashboard'))
-
-    tools = {
-        'rtl_fm': check_tool('rtl_fm'),
-        'multimon': check_tool('multimon-ng'),
-        'rtl_433': check_tool('rtl_433'),
+@app.route('/')
+def index() -> str:
+    if request.args.get('mode') == 'satellite':
+        return redirect(url_for('satellite.satellite_dashboard'))
+
+    tools = {
+        'rtl_fm': check_tool('rtl_fm'),
+        'multimon': check_tool('multimon-ng'),
+        'rtl_433': check_tool('rtl_433'),
         'rtlamr': check_tool('rtlamr')
     }
     devices = [d.to_dict() for d in SDRFactory.detect_devices()]
@@ -908,6 +908,7 @@ def health_check() -> Response:
         },
         'database': db_ok,
         'sdr_devices': sdr_count,
+        'sdr_claims': get_sdr_device_status(),
         'rate_limiting': _has_limiter,
         'processes': {
             'pager': current_process is not None and (current_process.poll() is None if current_process else False),