feat: @ottabase/backups — timestamped filenames, day-based retention, admin settings UI

[Copilot]

Implements @ottabase/backups with D1→R2 automated backup service and admin UI, then fixes several issues in the initial implementation: wrong filename format, missing day-based retention, no admin-configurable settings, and a route collision.

Core package (packages/backups/)

• Timestamped filenames: yyyy-mm-dd-hhmmss_appName.sql instead of {uuid}.sql
• Day-based retention: retentionDays config (rolling window) alongside existing count-based maxRetained
• appName config: Sourced from ottabase.config.ts, sanitized for filesystem safety
• Backward compat: deleteBackup/downloadBackup resolve keys for both legacy UUID and new timestamped formats via resolveBackupKey()

const service = createBackupService(env.OBCF_D1, env.OBCF_R2, {
  appName: 'my-app',     // → 2024-06-15-023000_my-app.sql
  retentionDays: 30,     // delete backups older than 30 days
  maxRetained: 30,       // also cap at 30 total
});

Admin API (worker/routes/admin-backups.ts)

• GET/PUT /api/admin/backups/settings — configure schedule (cron expression) and retention days
• Settings persisted in ScheduledTask model payload as { retentionDays }, read back during backup creation for enforcement consistency
• Route ordering fix: /settings matched before /:id regex catch-all

Admin UI (AdminBackupsPage.tsx)

• Settings panel: schedule presets dropdown + retention days input, creates/updates backup:database cron task
• Pending setup banner: shows actionable items when D1/R2/cron not configured, with inline "Configure →" link
• Download uses original timestamped filename

Tests

42 tests (8 new): generateBackupFilename, day-based retention pruning, new-format delete/download, backward compat with legacy keys.

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