chore: convert submodules to standard directories for true monorepo structure

vibn-frontend/app/api/admin/path-b/enable/route.ts

@@ -0,0 +1,17 @@
+import { NextResponse } from 'next/server';
+import { setFlag } from '@/lib/feature-flags';
+
+export async function POST(request: Request) {
+  const auth = request.headers.get('authorization') ?? '';
+  const bearer = auth.toLowerCase().startsWith('bearer ') ? auth.slice(7).trim() : '';
+  if (!bearer || !process.env.NEXTAUTH_SECRET || bearer !== process.env.NEXTAUTH_SECRET) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
+  }
+  await setFlag('path_b_disabled', false);
+  return NextResponse.json({
+    ok: true,
+    flag: 'path_b_disabled',
+    value: false,
+    note: 'Path B re-enabled.',
+  });
+}