feat: Tambahkan deep link handler untuk event confirmation

Deskripsi:
- Membuat route handler /event/[id]/confirmation untuk deep link mobile
- Menambahkan deteksi platform (iOS, Android, Web) dari user agent
- Memperbaiki Content-Type header untuk file .well-known (AASA & assetlinks)
- Menambahkan route ke public middleware agar bisa diakses tanpa auth

File yang diubah:
- src/app/event/[id]/confirmation/route.ts (baru)
- src/middleware.tsx (tambah public route)
- next.config.js (tambah headers untuk .well-known)

Testing:
- File .well-known accessible: ✅ YES
- Content-Type header correct: ✅ YES
- Deep link route works: ✅ YES
- Platform detection works: ✅ YES

### No Issue

next.config.js

@@ -16,6 +16,21 @@ const nextConfig = {
     }
     return config;
   },
+
+  async headers() {
+    return [
+      {
+        source: "/.well-known/:path*",
+        headers: [
+          { key: "Content-Type", value: "application/json" },
+          {
+            key: "Cache-Control",
+            value: "no-cache, no-store, must-revalidate",
+          },
+        ],
+      },
+    ];
+  },
 };
 
-module.exports = nextConfig;
+module.exports = nextConfig;