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/services/customer.service.js

@@ -0,0 +1,43 @@
+import { getDb } from '../db/client.js'
+
+const sql = getDb()
+
+export const createAnonymousCustomer = async ({ display_name }) => {
+  const [customer] = await sql`
+    INSERT INTO customers (display_name, is_anonymous)
+    VALUES (${display_name}, true)
+    RETURNING id, display_name, is_anonymous, created_at
+  `
+  return customer
+}
+
+export const linkCustomerAccount = async ({ customer_id, firebase_uid }) => {
+  const [existing] = await sql`
+    SELECT id, firebase_uid FROM customers WHERE id = ${customer_id}
+  `
+  if (!existing) throw Object.assign(new Error('Customer not found'), { code: 'NOT_FOUND', statusCode: 404 })
+  if (existing.firebase_uid) throw Object.assign(new Error('Account already linked'), { code: 'ALREADY_REGISTERED', statusCode: 409 })
+
+  // Also fetch phone from firebase_uid if exists in another customer record for uniqueness
+  const [firebaseLinked] = await sql`
+    SELECT id FROM customers WHERE firebase_uid = ${firebase_uid}
+  `
+  if (firebaseLinked) throw Object.assign(new Error('Account already linked'), { code: 'ALREADY_REGISTERED', statusCode: 409 })
+
+  const [updated] = await sql`
+    UPDATE customers
+    SET firebase_uid = ${firebase_uid}, is_anonymous = false
+    WHERE id = ${customer_id}
+    RETURNING id, display_name, is_anonymous, phone, created_at
+  `
+  return updated
+}
+
+export const getCustomerByFirebaseUid = async (firebase_uid) => {
+  const [customer] = await sql`
+    SELECT id, display_name, is_anonymous, phone, created_at
+    FROM customers
+    WHERE firebase_uid = ${firebase_uid}
+  `
+  return customer
+}