Show which Wi-Fi network (SSID) each tracked device is connected to.
The UniFi API already returns essid — this stores and displays it.

- Add current_ssid to tracked devices, ssid to connection history
- Display SSID in device table, detail modal, history, and CSV export
- Search filter includes SSID
- Schema repair covers upgrade edge cases
- Wi-Fi Stalker 0.11.4 → 0.12.0

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