Phase 1 scaffold: auth for all apps

- Backend: Fastify with two listeners (public + internal), routes, services, DB migration + seed
- client_app: Flutter with BLoC, all auth screens (welcome, display name, register, OTP, force-register)
- mitra_app: Flutter with BLoC, OTP-only login
- control_center: React + Vite, email/password login, mitra/user management, anonymity settings
- Docs: phase1 plan, API contract, client app mockup
- CLAUDE.md and shared memory for all subprojects

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

backend/src/plugins/firebase.js

@@ -0,0 +1,19 @@
+import admin from 'firebase-admin'
+
+let initialized = false
+
+export const initFirebase = () => {
+  if (initialized) return
+  admin.initializeApp({
+    credential: admin.credential.cert({
+      projectId: process.env.FIREBASE_PROJECT_ID,
+      clientEmail: process.env.FIREBASE_CLIENT_EMAIL,
+      privateKey: process.env.FIREBASE_PRIVATE_KEY?.replace(/\\n/g, '\n'),
+    }),
+  })
+  initialized = true
+}
+
+export const verifyFirebaseToken = async (token) => {
+  return admin.auth().verifyIdToken(token)
+}