Adds files_mcp/models.py (FileEntry, OperationResult) and
files_mcp/core/fs_ops.py with 9 pure file operations on already-resolved
Path objects: create/read/update/delete/list_dir/stat/search/move/copy.
All writes go through tempfile.mkstemp + os.replace for atomicity;
read enforces utf-8 + 1MB cap; create/update enforce strict presence
semantics (create: absent or overwrite; update: present). 39 unit tests
in tests/unit/test_fs_ops.py.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>