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/plugins/valkey.js

@@ -30,18 +30,24 @@ export const getValkeySub = () => {
 
 export const publish = async (channel, data) => {
   const pubClient = getValkeyPub()
-  await pubClient.publish(channel, JSON.stringify(data))
+  const numReceivers = await pubClient.publish(channel, JSON.stringify(data))
+  console.log(`[valkey] publish to ${channel} → ${numReceivers} receiver(s)`)
 }
 
 export const subscribe = (channel, callback) => {
   const subClient = getValkeySub()
   subClient.subscribe(channel)
-  subClient.on('message', (ch, message) => {
+  console.log(`[valkey] subscribed to ${channel}`)
+  const handler = (ch, message) => {
     if (ch === channel) {
+      console.log(`[valkey] received on ${channel}`)
       callback(JSON.parse(message))
     }
-  })
+  }
+  subClient.on('message', handler)
   return () => {
     subClient.unsubscribe(channel)
+    subClient.removeListener('message', handler)
+    console.log(`[valkey] unsubscribed from ${channel}`)
   }
 }