Full device backup and restore

[dirwin31]

Inspired by AngusBell97 and cherry picked work from Closed By Owner PR142

Summary:
Adds a Full Backup section to System Tools
Allow you to save your entire StarPilot setup to a file and restore it later on the same device, even after reinstalling, resetting, or switching forks.

Changes:

• Allows you to save device state as a zip file.
• Saves: settings profiles and toggle backups, FLM tunings and workspace, themes, calibration/learned tuning, driving stats, installed model list.
• Not saved: model files, API keys/accounts/credentials, Galaxy pairing and device identity, saved nav destinations, Wi-Fi/Bluetooth settings, driving recordings, offline maps, branch/OS.
• Reboot tracking now knows why the device is rebooting - from an update or from a restore
• Export and import are governed by device_backup_keys.json, which classifies every persistent Param as include or exclude; a test fails when a new Param is not classified. Credentials, pairing, navigation history, recordings, and model binaries are never included.
• Restores validate the archive and checksums, budget disk space, snapshot what they replace, and roll back from a recovery record on failure or interruption; Galaxy rolls back an interrupted restore at startup once parked.
• Saved models are re-downloaded through Model Manager after a restore, with an option to avoid downloading.
• Failed model download always releases its gate so it cannot strand later downloads or the restore flow.

Dependency: This branch builds on the update-page changes in #159

Verification:

• Device backup: 65 passed (test_device_backup.py)
• Backup restore integration: passed (test_device_backup_integration.py)
• Model re-download after restore: passed (test_restore_models.py)
• Mobile UI/System Tools front-end: passed (test_ui_vue_frontend.py)
• Failed-download recovery: 7 passed (test_download_failure_recovery.py)
• Backup restore UI (node): passed (test_device_backup_frontend.cjs)
• Update/branch selector (node): 30 passed (test_branch_selector.mjs)
• Combined targeted run: 137 passed, 0 failed