Removes the debounced auto-save (useAutoSave hook) which was causing the
editor to reload previous content. Replaces it with explicit save on
Cmd+S (⌘S), consistent with the git-based UX of the app.
- Removed useAutoSave hook and its debounce mechanism
- Added useSaveNote hook for direct persist-to-disk
- Added useEditorSave hook that manages pending content buffer + save
- Cmd+S now persists the current editor content immediately
- Rename-before-save: saves pending content before rename to prevent
the "Failed to rename note" error
- Updated E2E test to verify Cmd+S behavior
- 471 tests passing, code health gates passed
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
