fix: add .dockerignore and src volume mount for live code sync

Add .dockerignore to exclude __pycache__, .venv, test artifacts, and
other host-only files from Docker build context. Prevents stale .pyc
cache pollution in container images.

Add read-only bind mount for ./apps/api/src:/app/src in docker-compose.yml
so code changes on the host are reflected in the running container
without requiring image rebuild. This is a dev convenience that resolves
the persistent 'tool_configs' import error from stale container images.

Quality gates: docker-compose.yml syntax valid, .dockerignore parsed.

docker-compose.yml

@@ -64,6 +64,7 @@ services:
       - /data/repos:/data/repos
       - /data/working-copies:/data/working-copies
       - /data/instances:/data/instances
+      - ./apps/api/src:/app/src:ro
     ports:
       - "8000:8000"
     depends_on: