chore: exclude coverage temp files and add no cover annotation

- Add *.cover to .gitignore to exclude coverage temp files
- Add 'pragma: no cover' to _validate_environment placeholder method

Author: Yoshihiro Takahara

.gitignore

@@ -35,6 +35,8 @@ ENV/
 *.swo
 
 # Testing
+*.cover
+*,cover
 .coverage
 .coverage.*
 .pytest_cache/

src/mcp_text_editor/text_editor.py

@@ -49,7 +49,7 @@ def _validate_environment(self) -> None:
         Can be extended to check for specific permissions or configurations.
         """
         # Future: Add environment validation if needed
-        pass
+        pass  # pragma: no cover
 
     def _validate_file_path(self, file_path: str | os.PathLike) -> None:
         """