Phase 2 refinements: Firebase config, dev environment fixes, phase 3 requirement draft

- Integrated Firebase SDK in both Flutter apps (google-services, firebase_options)
- Fixed auth flow, API client, and pairing/status blocs for dev environment
- Added full Flutter project scaffolds (android, ios, web, etc.)
- Added phase 3 chat engine requirement document
- Added bugreport zip pattern to gitignore

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

backend/src/services/customer.service.js

@@ -2,10 +2,17 @@ import { getDb } from '../db/client.js'
 
 const sql = getDb()
 
-export const createAnonymousCustomer = async ({ display_name }) => {
+export const createAnonymousCustomer = async ({ display_name, firebase_uid }) => {
+  // Return existing customer if already linked to this Firebase UID
+  const [existing] = await sql`
+    SELECT id, display_name, is_anonymous, created_at
+    FROM customers WHERE firebase_uid = ${firebase_uid}
+  `
+  if (existing) return existing
+
   const [customer] = await sql`
-    INSERT INTO customers (display_name, is_anonymous)
-    VALUES (${display_name}, true)
+    INSERT INTO customers (display_name, is_anonymous, firebase_uid)
+    VALUES (${display_name}, true, ${firebase_uid})
     RETURNING id, display_name, is_anonymous, created_at
   `
   return customer