refactor: store workspaces as {workspace_id}/{repo_name} for natural git clone layout

Working copies were stored as /data/working-copies/{repo_id}/{workspace_name}/,
so git clone was forced into a user-named directory. That meant the container
mount basename was the workspace name (e.g. main) instead of the repo name.

- Generate the workspace UUID before cloning and clone into
  /data/working-copies/{workspace_id}/ so git creates {repo_name}/ naturally
- Set workspace.path to /data/working-copies/{workspace_id}/{repo_name}/
- Update _migrate_clone_into_workspace() to use the same layout
- _get_repository_mount_name() now prefers workspace.path basename and only
  falls back to remote URL / repo.name for legacy repo-only instances
- Update unit tests to assert workspace path basename is used for mounts

Quality gates:
- pytest tests/unit: 219 passed
- ruff: clean on changed files
- mypy: clean on changed files

.pi-map.index.md

@@ -16,7 +16,7 @@ dir: .
 Trust boundary: index routes, map orients, source decides.
 
 ## role
-Infrastructure and deployment configuration for a self-hosted project management platform with containerized services, SSO integration, and reverse proxy support.
+A self-hosted project management and git repository platform with OAuth2 authentication, providing containerized deployment via Docker Compose.
 ## parent
 -
 ## children