feat: add authentication to L1 server

- Runs require auth token (verified with L2)
- Store username with each run
- UI login/register/logout via L2
- Filter runs by logged-in user
- Cookie-based auth for UI

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

docker-compose.yml

@@ -17,6 +17,7 @@ services:
     environment:
       - REDIS_URL=redis://redis:6379/5
       - CACHE_DIR=/data/cache
+      - L2_SERVER=http://activitypub_l2-server:8200
     volumes:
       - l1_cache:/data/cache
     depends_on: