Annotate file history entries with matches_working_tree and surface that
information in the UI so the most recent commit can be identified as
"current version" when its content equals the working tree.
- Backend: add FileHistoryCommit and annotate_file_history(...) which checks
(only for regular files) whether the newest commit's blob matches the
working tree via `git diff --quiet`. list_file_history now returns the
annotated commits.
- Types: add optional matches_working_tree to GitCommit shape used by the UI.
- UI: show a "Current version"/"Aktueller Stand" badge and disable Diff/Restore
actions for entries that match the working tree (text localized for de/en).
Also add a test that verifies the matching behavior across file edits,
staging, committing and deletion. No external API breaking changes.
Christoph
096f62907c