feat: implement responsive spacing improvements
- Add CSS custom properties for spacing scale (4px base), breakpoints, and fluid typography
- Create layout utilities: Container, Stack, Row, Grid
- Update AppShell with responsive mobile navigation
- Update card grid with responsive columns
- Update dialogs with viewport-aware sizing and mobile fullscreen
- Update workspace layout for mobile stacking
- Ensure minimum 44px touch targets for buttons
- Add table-responsive and text truncation utilities
- Update page headers for mobile stacking
Quality gates: typecheck ✓, lint ✓, build ✓
Fusion
2b5331a1a0