Implement keyboard navigation system #45
Description
Add comprehensive keyboard controls for TUI navigation.
Requirements
- Arrow keys for navigation
- Tab to switch between panels
- Shortcuts for common actions
- Help screen with key bindings
- Vi-style navigation support
- Context-sensitive controls
Acceptance Criteria
- Arrow keys navigate between printers
- Tab cycles through UI sections
- 'h' shows help screen with all shortcuts
- Number keys quick-jump to printer
- '/' for search/filter functionality
- Shortcuts shown in status bar