Add configurable backup schedule with admin UI

- Make backup frequency (6h/12h/1d/7d), time, and day-of-week
  configurable via settings, stored in appSettings key-value table
- Add rescheduleBackup() to dynamically update cron job at runtime
- Differentiate manual (sofa-manual-*) vs scheduled (sofa-scheduled-*)
  backup filenames with source icons and tooltips in the backup list
- Pruning now only targets scheduled backups, leaving manual ones intact
- Merge backup-actions.ts into actions.ts, use shadcn DropdownMenu for
  all selectors (consistent with dashboard stats cards)
- Fix hydration mismatch on relative backup timestamps

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

app/(pages)/settings/page.tsx

@@ -64,6 +64,15 @@ export default async function SettingsPage() {
   const maxBackupRetention = isAdmin
     ? Number.parseInt(getSetting("maxBackupRetention") ?? "7", 10)
     : 7;
+  const backupFrequency = isAdmin
+    ? (getSetting("backupScheduleFrequency") ?? "1d")
+    : "1d";
+  const backupTime = isAdmin
+    ? (getSetting("backupScheduleTime") ?? "02:00")
+    : "02:00";
+  const backupDow = isAdmin
+    ? Number.parseInt(getSetting("backupScheduleDow") ?? "0", 10)
+    : 0;
 
   const repoUrl = "https://github.com/jakejarvis/sofa";
 
@@ -129,6 +138,9 @@ export default async function SettingsPage() {
                 initialBackups={backups}
                 initialScheduledEnabled={scheduledBackupsEnabled}
                 initialMaxRetention={maxBackupRetention}
+                initialFrequency={backupFrequency as "6h" | "12h" | "1d" | "7d"}
+                initialTime={backupTime}
+                initialDow={backupDow}
               />
             </Card>
           </div>