Salvage follow-up to the cherry-picked feat/test commits:
- W1: the unpack/install update path in main.py printed the
'~ N user-modified (kept)' notice without the new
'hermes skills list-modified' hint that the git-pull path got.
Mirror the hint to both sites so the count is actionable
regardless of which update path runs.
- W2: 'hermes skills diff <name>' (bundled-vs-stock) now shares the
verb with the gateway write-approval 'diff <id>'. The gateway
handler's docstring + truncation message pointed users to
'/skills diff <id>' on the CLI, which now resolves a bundled skill
by that name instead. Point at the pending JSON file and note the
two diff commands are distinct.
- Add an invariant test asserting every 'user-modified (kept)' notice
in main.py carries the discovery hint (guards sibling drift).
