🐛 fix(firebase): add fallback values so build succeeds without env vars

Fork PR builds fail with auth/invalid-api-key because GitHub Actions
doesn't expose secrets to fork PRs. Add dummy fallback values in
Firebase config so static export succeeds without real keys.
Also add .env.example for contributors.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: lwinmoepaing

.env.example

@@ -0,0 +1,11 @@
+# Firebase Configuration
+# Copy this file to .env.local and fill in your values
+# Get these from Firebase Console → Project Settings → General → Your apps
+
+NEXT_PUBLIC_FIREBASE_API_KEY=
+NEXT_PUBLIC_FIREBASE_AUTH_DOMAIN=
+NEXT_PUBLIC_FIREBASE_PROJECT_ID=
+NEXT_PUBLIC_FIREBASE_STORAGE_BUCKET=
+NEXT_PUBLIC_FIREBASE_MESSAGING_SENDER_ID=
+NEXT_PUBLIC_FIREBASE_APP_ID=
+NEXT_PUBLIC_FIREBASE_MEASUREMENT_ID=

src/lib/firebase/config.ts

@@ -4,13 +4,13 @@ import { getFirestore, type Firestore } from "firebase/firestore";
 import { getStorage, type FirebaseStorage } from "firebase/storage";
 
 const firebaseConfig = {
-  apiKey: process.env.NEXT_PUBLIC_FIREBASE_API_KEY,
-  authDomain: process.env.NEXT_PUBLIC_FIREBASE_AUTH_DOMAIN,
-  projectId: process.env.NEXT_PUBLIC_FIREBASE_PROJECT_ID,
-  storageBucket: process.env.NEXT_PUBLIC_FIREBASE_STORAGE_BUCKET,
-  messagingSenderId: process.env.NEXT_PUBLIC_FIREBASE_MESSAGING_SENDER_ID,
-  appId: process.env.NEXT_PUBLIC_FIREBASE_APP_ID,
-  measurementId: process.env.NEXT_PUBLIC_FIREBASE_MEASUREMENT_ID,
+  apiKey: process.env.NEXT_PUBLIC_FIREBASE_API_KEY || "dummy-key",
+  authDomain: process.env.NEXT_PUBLIC_FIREBASE_AUTH_DOMAIN || "localhost",
+  projectId: process.env.NEXT_PUBLIC_FIREBASE_PROJECT_ID || "demo-project",
+  storageBucket: process.env.NEXT_PUBLIC_FIREBASE_STORAGE_BUCKET || "",
+  messagingSenderId: process.env.NEXT_PUBLIC_FIREBASE_MESSAGING_SENDER_ID || "",
+  appId: process.env.NEXT_PUBLIC_FIREBASE_APP_ID || "",
+  measurementId: process.env.NEXT_PUBLIC_FIREBASE_MEASUREMENT_ID || "",
 };
 
 // Singleton Firebase app