Mirror of the SDK's FsToolName literal members.
Hardcoded here rather than derived from deepagents.FsToolName because
deepagents must not be imported on the arg-parsing hot path (see AGENTS.md
"Startup performance"); this module is dependency-free and safe for main.py to
import. Consumers (main._parse_allow_fs_tools_flag,
tool_catalog.collect_built_in_tools) alias this set, and get_args(FsToolName)
drift guards in test_main_args and test_tool_catalog pin it so a new or
renamed SDK filesystem tool fails a test instead of silently diverging.
