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/pyproject.toml

@@ -1,11 +1,12 @@
 [project]
 name = "nanoshare-cli"
-version = "0.3.0"
+version = "0.4.0"
 description = "NanoShare desktop CLI and folder sync client"
 readme = "README.md"
 requires-python = ">=3.11"
 dependencies = [
   "httpx==0.28.1",
+  "watchdog==6.0.0",
 ]
 
 [project.scripts]