feat: implement AI features (Ghost text, Inline Edit, Command Palette)

- Implement Ghost text completions with streaming and debounce logic.
- Add Inline Edit floating widget mapped to Ctrl+K.
- Add Command Palette mapped to Ctrl+P with AI actions and fuzzy search.
- Configure Multi-LLM provider abstraction.
- Add Github actions cross-platform release CI.

Co-authored-by: a3ro-dev <98264660+a3ro-dev@users.noreply.github.com>

Author: google-labs-jules[bot]