Add .env.example and adjust .gitignore for env file handling

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,4 @@
+MQTT_BROKER=nuccy
+MQTT_PORT=1882
+MQTT_USER=rxf
+MQTT_PASSWORD=your_password_here

.gitignore

@@ -31,7 +31,9 @@ yarn-error.log*
 .pnpm-debug.log*
 
 # env files (can opt-in for committing if needed)
-.env*
+.env
+.env.local
+.env.*.local
 
 # vercel
 .vercel