feat(backup): add ZIP export endpoint (DB + images)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/routes/api/admin/backup/+server.ts

@@ -0,0 +1,18 @@
+import type { RequestHandler } from './$types';
+import { createBackupStream, backupFilename } from '$lib/server/backup/export';
+import { Readable } from 'node:stream';
+
+const DB_PATH = process.env.DATABASE_PATH ?? './data/kochwas.db';
+const IMAGE_DIR = process.env.IMAGE_DIR ?? './data/images';
+
+export const GET: RequestHandler = async () => {
+  const archive = createBackupStream({ dbPath: DB_PATH, imagesDir: IMAGE_DIR });
+  const filename = backupFilename();
+  return new Response(Readable.toWeb(archive) as ReadableStream, {
+    status: 200,
+    headers: {
+      'content-type': 'application/zip',
+      'content-disposition': `attachment; filename="${filename}"`
+    }
+  });
+};