feat: UAT environment setup with separate PocketBase instance

- Add UAT PocketBase on port 8712 with separate pb_data_uat
- Add UAT nginx config proxying to UAT PB (port 8712)
- Update Dockerfile to support NGINX_CONF build arg
- Add .gitignore for .playwright-mcp/
- Auto-generated team_sessions migration

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitignore

@@ -35,4 +35,4 @@ backend/pb_migrations.bak/
 
 # Temporary files
 *.tmp
-.cache/
+.cache/.playwright-mcp/