dumbgit v0.18.1

Compare view improvements:

• Click anywhere on the overview track to jump to the corresponding position.
• Size overview change markers to match the actual changed rows.
• Keep the viewport indicator visible over change markers with a neutral white overlay.
• Hide the native diff scrollbar for a cleaner reader.

Validation: CI passed, including tests, TypeScript checks, build, and npm package smoke test.

Full changelog: v0.18.0...v0.18.1