Cleanup pass on the salvage (behavior-preserving):
- diff_bundled_skill now uses the existing _skill_file_list() helper
instead of reimplementing the rglob/is_file/relative_to file-set
enumeration inline (twice).
- Extract _is_tracked_user_modification(origin_hash, user_hash) and use
it in BOTH the sync loop and list_user_modified_bundled_skills() so the
'kept user edit' rule can't drift between the two sites.
- _read_text_for_diff -> _read_for_diff returns (bytes, text); the binary
branch now compares the bytes it already read instead of re-reading
both files from disk.
- Drop the unused 'user_present' key from diff_bundled_skill's return
contract (no consumer or test ever read it).
- test_update_modified_notice: drop the brittle '>= 2 sites' count-floor
so consolidating the two print paths into a shared helper stays a
welcome refactor; keep the per-site 'count notice => discovery hint'
invariant (still mutation-tested).
f6fac60e66