force quit

fix: tab

feat: enable multi-window support with smart file handling

- Refactor `src/main/index.ts` to support opening multiple
  documents in separate windows.
- Implement `windowFiles` tracking to prevent opening
  duplicate windows for the same file; focuses existing
  window instead.
- Update `second-instance` handler to spawn new
  windows for new files.
- Make IPC handlers (`save-file`, window controls) context-aware using `event.sender`.
- Update `GEMINI.md` with architecture improvements.

Merge branch 'main' of https://github.com/fezcode/Nocturnote

feat: line ending converter.