Revive project at new apartment — fixes, SSID update, gitignore

WiFi/firmware:
- SSID updated to botnet in both node and ble_node config.h
- Stale coordinator comment removed from node/config.h

Coordinator fixes:
- BLE-only nodes now visible in dashboard sidebar and node detail
  (build_nodes was querying beacon_events only; BLE nodes have no beacons)
- ble_events and heartbeat_events added to pruning cycle
- ble_events table added to ensure_schema() in dashboard
- confidence column dropped from beacon_events (always 'high', never queried)
- Ingestor commits batched per packet instead of per store call
- wal_autocheckpoint=500 added to ingestor DB connection (writer was missing it)
- python3 -u added to both service ExecStart lines (stdout was buffered,
  logs not appearing in journalctl)

Repo hygiene:
- .gitignore added (events.db, __pycache__, build artifacts)
- events.db removed from git tracking
- README updated: new apartment, node table, active investigations,
  BLE observations labelled as previous-location data, status checklist

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

coordinator/dashboard.service

@@ -5,7 +5,7 @@ After=network.target
 [Service]
 Type=simple
 WorkingDirectory=/opt/esp32_cluster/coordinator
-ExecStart=/usr/bin/python3 dashboard.py
+ExecStart=/usr/bin/python3 -u dashboard.py
 Restart=always
 RestartSec=5
 StandardOutput=journal