* feat(chat): add arrow key navigation for thinking mode in model selector
Adds keyboard arrow key navigation for thinking mode selection within the model picker, enabling a fully keyboard-driven workflow for model and variant selection.
Changes:
- Model Selector: Added ←/→ arrow key handling to cycle thinking variants while picker is open
- Introduced transient state to track per-model variant selections during picker lifecycle
- Updated metadata display logic to show thinking mode only after adjustment with arrow keys
- Added contextual footer hints that appear only when highlighted model supports thinking variants
- Modified Enter key behavior to apply both selected model and pending thinking variant together
- Help Dialog: Added in-picker navigation shortcuts (↑↓ navigate, ←→ adjust thinking)
- Documentation: Updated CHANGELOG.md files with feature entry
Behavior:
- Navigate models with ↑↓, adjust thinking with ←→, press Enter to apply both
- Footer hints update dynamically based on highlighted model capabilities
- Thinking display persists only for models adjusted with arrow keys
- No-op for models without variants (clean, no feedback)
Testing:
- Type-check, lint, and build all pass
- Manual testing verified on dev server