feat(cli): add private NanoShare sync client

- Add a separate installable NanoShare CLI package under cli/.
- Implement browser login with local callback and refresh-token config.
- Add upload, list, download, sync, and watch CLI commands.
- Add private owner-only file download endpoint for CLI downloads.
- Add CLI auth endpoints for browser login and token refresh.
- Return file_id from ServiceLink uploads for reliable sync state.
- Exclude the CLI package from NanoShare container builds.
- Include tests for private downloads and sync state updates.

cli/nanoshare_client/__main__.py

@@ -0,0 +1,8 @@
+from __future__ import annotations
+
+import sys
+
+from .cli import main
+
+if __name__ == '__main__':
+  sys.exit(main())