cleanup and rename provider to plugin

plugins/hello/__init__.py

@@ -5,7 +5,7 @@ This minimal plugin demonstrates the typical hooks a plugin may implement:
 - `search()` to return `SearchResult` items
 - `download()` to persist a sample file (useful for local tests)
 
-See `docs/provider_guide.md` for authoring guidance.
+See `docs/plugin_guide.md` for authoring guidance.
 """
 
 from __future__ import annotations
@@ -13,7 +13,7 @@ from __future__ import annotations
 from pathlib import Path
 from typing import Any, Dict, List, Optional
 
-from ProviderCore.base import Provider, SearchResult
+from PluginCore.base import Provider, SearchResult
 
 
 class HelloProvider(Provider):