Switch BLE scanner to active mode — bleak 0.20 passive requires or_patterns on BlueZ

Passive mode fails on Debian bookworm bleak 0.20.2 without or_patterns filter.
Active mode is functionally equivalent for building-level presence detection
and actually yields more complete advertisement data including device names.

net_alerter/ble_alerter.py

@@ -256,8 +256,8 @@ async def scan_loop():
         
         await on_arrival(name, mac, rssi)
     
-    # Passive scanner — no SCAN_REQ packets sent
-    async with BleakScanner(detection_callback=detection_callback, scanning_mode="passive") as scanner:
+    # Active scanner — sends SCAN_REQ to get full advertisement data including device names
+    async with BleakScanner(detection_callback=detection_callback) as scanner:
         try:
             while not shutdown_event.is_set():
                 await asyncio.sleep(1)