Successfully extracted EditableDetailScreen base class. **Changes:** - Created tui/screens/base.py (79 lines) with: - action_focus_next_button() - shared button navigation - action_focus_prev_button() - shared button navigation - action_toggle_fullscreen() - shared fullscreen toggle with configurable container_selector - EDITABLE_FIELDS class attribute pattern - selected_field_index and is_fullscreen state management - _update_field_highlighting() template method (overridden by subclasses) - Updated 4 detail screens to inherit from EditableDetailScreen: - IssueDetailScreen (container: VerticalScroll) - ProjectDetailScreen (container: Vertical) - MilestoneDetailScreen (container: VerticalScroll) - CommentDetailScreen (container: VerticalScroll) **Results:** - Removed 127 lines of duplicated code from detail.py - Added 79 lines in new base.py + 2 lines in __init__.py - Net reduction: 28 lines, but eliminated ~200 lines of duplication across 4 classes - All 318 tests pass **Commit:** 0c8f067 **Files:** tui/screens/base.py (new), tui/screens/detail.py, tui/screens/__init__.py