feat: Add battle screen with real-time sync (Phase 1 MVP)

- Add battle module with sessions, maps, tokens, and combatants
- Implement WebSocket gateway for real-time battle updates
- Add map upload with configurable grid system
- Create battle canvas with token rendering and drag support
- Support PC tokens from characters and NPC tokens from templates
- Add initiative tracking and round management
- GM-only controls for token manipulation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server/package.json

@@ -38,6 +38,7 @@
     "@nestjs/passport": "^11.0.5",
     "@nestjs/platform-express": "^11.0.1",
     "@nestjs/platform-socket.io": "^11.1.12",
+    "@nestjs/serve-static": "^5.0.4",
     "@nestjs/swagger": "^11.2.5",
     "@nestjs/websockets": "^11.1.12",
     "@prisma/adapter-pg": "^7.2.0",