feat: add config API and update ApkList to use configured tabs

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

app/api/config/route.ts

@@ -0,0 +1,8 @@
+import { NextResponse } from 'next/server';
+import { APK_TABS } from '@/lib/constants';
+
+export async function GET() {
+  return NextResponse.json({
+    tabs: APK_TABS,
+  });
+}