chore(python): audit plugins shared modules

_managed_files owns the file snapshot reader and public metadata helpers used by pinned directories, durable copies, and opaque snapshots; transaction staging owns read_target and same_identity_and_contents; dead helpers removed; hook_template no longer re-exports the guard generator; mypy targets win32 so _windows_security type-checks.

Claude-Session: https://claude.ai/code/session_01Agoc9bRVE9KL7mmWtey9Vq

pyproject.toml

@@ -47,3 +47,6 @@ elydora = ["py.typed"]
 
 [tool.setuptools.dynamic]
 version = {attr = "elydora._version.__version__"}
+
+[tool.mypy]
+platform = "win32"