feat(backup): add containerarchive-backed backup storage, restore, download, and pruning support

ts/database/migrations/migration-014-containerarchive.ts

@@ -0,0 +1,13 @@
+import { BaseMigration } from './base-migration.ts';
+import type { TQueryFunction } from '../types.ts';
+
+export class Migration014ContainerArchive extends BaseMigration {
+  readonly version = 14;
+  readonly description = 'Add containerarchive snapshot tracking to backups';
+
+  up(query: TQueryFunction): void {
+    query('ALTER TABLE backups ADD COLUMN snapshot_id TEXT');
+    query('ALTER TABLE backups ADD COLUMN stored_size_bytes INTEGER DEFAULT 0');
+    query('CREATE INDEX IF NOT EXISTS idx_backups_snapshot ON backups(snapshot_id)');
+  }
+}