feat: add BLE Radar database import

- Add import_ble_radar.py module for importing BLE Radar exports
- Add /api/import/ble-radar endpoint for file upload
- Add import section to dashboard with file picker
- CLI: python -m rf_mapper.import_ble_radar <file.sqlite>
- Imports devices, RSSI, favorites, and custom labels

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

config.yaml

@@ -1,6 +1,6 @@
 gps:
-  latitude: 50.85846541332012
-  longitude: 4.397570348817993
+  latitude: 50.858532461583906
+  longitude: 4.397587773133864
 web:
   host: 0.0.0.0
   port: 5000
@@ -12,7 +12,6 @@ scanner:
   longitude: null
   floor: null
   is_master: true
-  bt_mac: '2C:CF:67:6F:66:AC'
   wifi_interface: wlan0
   bt_scan_timeout: 10
   path_loss_exponent: 2.5