Add GitHub profile backup feature

New feature to automatically backup K-profiles, cloud profiles, and app
settings to a GitHub repository with scheduled or on-demand execution.

Features:
- Configure GitHub repo URL and Personal Access Token
- Schedule backups hourly, daily, or weekly (background scheduler)
- Manual backup trigger with real-time progress tracking
- Skip unchanged commits (only creates commit when data changes)
- Backup history log with status and commit links
- Requires Bambu Cloud login for full profile access
- New Settings → Backup & Restore tab consolidating all backup options
- GitHub backup config included in local backup/restore (except PAT)

Backend:
- New models: GitHubBackupConfig, GitHubBackupLog
- New service: GitHubBackupService with scheduler and GitHub API client
- New routes: /github-backup/* for config, status, logs, and triggers
- Updated settings.py to include github_backup in backup/restore

Frontend:
- New GitHubBackupSettings.tsx component with auto-save
- Updated SettingsPage with Backup tab and status indicator
- Added API types and methods to client.ts

Tests:
- Backend integration tests for all GitHub backup API endpoints
- Frontend API type and endpoint tests

backend/app/core/database.py

@@ -38,6 +38,7 @@ async def init_db():
         archive,
         external_link,
         filament,
+        github_backup,
         kprofile_note,
         library,
         maintenance,