- Add `persistence.rs` for stable serialization of dock layouts without runtime identifiers.
- Introduce `preview.rs` for geometry handling of dock drop previews.
- Create `sizing.rs` to manage content-aware sizing policies and constraint solving for dock panels.
- Implement `welcome.rs` to provide a welcome surface when no documents are open, featuring New and Open actions.
- Add Inverse selection (Shift+Ctrl+I) with engine.invert_selection()
- Add Shrink, Feather, Border, Smooth menu items with parameter dialogs
- Implement selection_border() and selection_smooth() in engine API
- Implement border_mask() and smooth_mask() in hcie-selection crate
- Update SelectionOpApply handler for all selection operations