Add missing migration for spoolbuddy update_status columns

  The OTA update feature added update_status and update_message to the
  SpoolBuddyDevice model but no ALTER TABLE migration, causing
  "no such column: spoolbuddy_devices.update_status" on existing databases.

CHANGELOG.md

@@ -12,6 +12,7 @@ All notable changes to Bambuddy will be documented in this file.
 
 ### Fixed
 - **SpoolBuddy Daemon Reports Stale Version** — The SpoolBuddy daemon maintained its own hardcoded `__version__` that was never bumped to `0.2.3b1`, causing the update check to incorrectly show an update from `0.2.2b1` to the latest release. Fixed by reading the version at import time from the backend's `APP_VERSION` in `backend/app/core/config.py` — the single source of truth — so the daemon version is always in sync.
+- **SpoolBuddy Update Columns Missing from Database** — The OTA update feature added `update_status` and `update_message` to the device model but was missing the database migration, causing "no such column" errors on existing installations.
 - **Queue Print Command Not Reaching Printer** ([#778](https://github.com/maziggy/bambuddy/issues/778)) — When a queue item targeted a specific printer and the scheduler's power-on-wait loop triggered, each reconnection attempt created a new MQTT client that re-attempted subscribing to the request topic. On printers whose broker rejects this subscription (e.g. A1), this caused repeated connect/disconnect cycles for up to 170 seconds, leaving the MQTT connection in a fragile state where the print command could silently fail to reach the printer. Fixed by caching request topic support state per serial number at the class level, so new client instances skip the subscription immediately instead of rediscovering the rejection. Reported by @RubenKremer.
 - **AMS Slot Search Shows Unrelated Profiles** ([#681](https://github.com/maziggy/bambuddy/issues/681)) — Searching for a non-existent filament profile in the AMS slot configuration showed unrelated profiles instead of an empty result. The saved preset bypassed the search filter entirely, so stale mappings (e.g. a slot previously configured with "Bambu PLA Matte" that now holds a Silk spool) would always appear regardless of the search query. The saved preset now only bypasses the printer model filter, not the search filter. Reported by @RosdasHH.
 - **Virtual Printer FTP Routed to Wrong VP** ([#735](https://github.com/maziggy/bambuddy/issues/735)) — When running multiple virtual printers with different access codes on separate bind IPs, FTP connections were routed to the wrong VP. Root cause: the iptables `REDIRECT` rule rewrites the destination IP to the incoming interface's primary address, so all FTP traffic went to the first VP regardless of the intended target. Fix: FTP server now binds directly to port 990 (standard implicit FTPS), eliminating the need for iptables redirect. Requires `CAP_NET_BIND_SERVICE` (already set in the systemd service and Docker image). Also removed a global `set_exception_handler()` in the MQTT server that caused spurious error messages when running multiple VPs. See `docs/migration-vp-ftp-port.md` for migration steps. Reported by @VREmma.