feat: L1 server URL sent with publish request (many-to-many support)

- Add l1_server field to RecordRunRequest
- L2 fetches run data from the specified L1 URL instead of hardcoded config
- Store l1_server in provenance and metadata
- Remove ARTDAG_L1 config requirement from L2
- Update docker-stack.yml comments

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

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

docker-stack.yml

@@ -29,7 +29,7 @@ services:
     environment:
       - REDIS_URL=redis://redis:6379/5
       - CACHE_DIR=/data/cache
-      # L2_SERVER and L2_DOMAIN from .env file
+      # L1_PUBLIC_URL, L2_SERVER, L2_DOMAIN from .env file
     volumes:
       - l1_cache:/data/cache
     depends_on:
@@ -69,7 +69,7 @@ services:
       - .env
     environment:
       - ARTDAG_DATA=/data/l2
-      # ARTDAG_DOMAIN, ARTDAG_USER, ARTDAG_L1, JWT_SECRET from .env file
+      # ARTDAG_DOMAIN, ARTDAG_USER, JWT_SECRET from .env file
     volumes:
       - l2_data:/data/l2
     depends_on: