choredocker): enhance local Docker socket access and error handling

- Added guidance for Docker socket group access in docker-compose files.
- Introduced docker-compose.override.example.yml for supplemental group configuration.
- Improved entrypoint diagnostics to include socket GID and group guidance.
- Updated README with instructions for setting up Docker socket access.
- Enhanced backend error handling to provide actionable messages for permission issues.
- Updated frontend components to display troubleshooting information regarding Docker socket access.
- Added tests to ensure proper error messages and guidance are rendered in UI.
- Revised code coverage settings to include Docker service files for better regression tracking.

.docker/compose/docker-compose.local.yml

@@ -27,6 +27,8 @@ services:
       - FEATURE_CERBERUS_ENABLED=true
       # Emergency "break-glass" token for security reset when ACL blocks access
       - CHARON_EMERGENCY_TOKEN=03e4682c1164f0c1cb8e17c99bd1a2d9156b59824dde41af3bb67c513e5c5e92
+    # Docker socket group access: copy docker-compose.override.example.yml
+    # to docker-compose.override.yml and set your host's docker GID.
     extra_hosts:
       - "host.docker.internal:host-gateway"
     cap_add: