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>

backend/pb_migrations/1776480499_updated_team_sessions.js

@@ -0,0 +1,22 @@
+/// <reference path="../pb_data/types.d.ts" />
+migrate((db) => {
+  const dao = new Dao(db)
+  const collection = dao.findCollectionByNameOrId("sac8t6o9rspld8p")
+
+  collection.listRule = "@request.auth.id != \"\""
+  collection.viewRule = "@request.auth.id != \"\""
+  collection.updateRule = "@request.auth.id != \"\""
+  collection.deleteRule = "@request.auth.id != \"\""
+
+  return dao.saveCollection(collection)
+}, (db) => {
+  const dao = new Dao(db)
+  const collection = dao.findCollectionByNameOrId("sac8t6o9rspld8p")
+
+  collection.listRule = "sourceGroup.owner = @request.auth.id || sourceGroup.members.id = @request.auth.id"
+  collection.viewRule = "sourceGroup.owner = @request.auth.id || sourceGroup.members.id = @request.auth.id"
+  collection.updateRule = "sourceGroup.owner = @request.auth.id"
+  collection.deleteRule = "sourceGroup.owner = @request.auth.id"
+
+  return dao.saveCollection(collection)
+})