Follow-up to PR #862 (local skills classification by arceus77-7):
- Remove unnecessary isinstance guard on _read_manifest() return value —
it always returns Dict[str, str], so set() on it suffices.
- Extract repeated hub-dir monkeypatching into a shared pytest fixture (hub_env).
- Add three_source_env fixture for source-classification tests.
- Add _read_manifest monkeypatch to test_do_list_initializes_hub_dir
(was fragile — relied on empty skills list masking the real manifest).
- Add test coverage for --source hub and --source builtin filters.
- Extract _capture() helper to reduce console/StringIO boilerplate.
5 tests, all green.
Call ensure_hub_dirs() at the start of hermes skills list so the\nSkills Hub directory structure is created before reading hub\nmetadata.\n\nAdd a regression test covering the empty-home path where\ndoctor recommends running the list command.\n\nRefs: #703
