feat(cli): watch files with event streams

- Add a private SSE endpoint that emits file change events for authenticated clients.
- Replace the watch sleep loop with watchdog local file events and remote SSE triggers.
- Debounce local event bursts and keep watch running after transient sync failures.
- Add watchdog as a standalone CLI dependency and cover watch behavior in tests.
- Bump NanoShare to 1.25.0 and the standalone CLI to 0.4.0.

cli/nanoshare_client/client.py

@@ -45,11 +45,17 @@ def list_remote(client, node: str) -> list[dict]:
   files = result.get('files', []) if isinstance(result, dict) else []
   return files if isinstance(files, list) else []
 
-def download_url(client, node: str, file_id: str) -> str:
+def node_url(client, node: str, path: str) -> str:
   base = client.registry.get(node)
   if not base:
     raise RuntimeError(f'unknown node: {node}')
-  return f"{base.rstrip('/')}/api/files/{quote(file_id, safe='')}/download"
+  return f"{base.rstrip('/')}{path}"
+
+def download_url(client, node: str, file_id: str) -> str:
+  return node_url(client, node, f"/api/files/{quote(file_id, safe='')}/download")
+
+def events_url(client, node: str) -> str:
+  return node_url(client, node, '/api/files/events')
 
 def download(client, node: str, file_id: str, path: Path) -> None:
   path.parent.mkdir(parents=True, exist_ok=True)