**Layout Components:**
- AppLayout.vue: Responsive grid layout (sidebar + main + footer)
- Sidebar.vue: Collapsible navigation (256px → 64px), smooth animation
- Header.vue: Top bar with theme toggle + user menu + notifications
- Footer.vue: System status indicator + quick links + version info
**Theme System Enhancements:**
- tokens.css: Explicit dark mode via data-theme attribute
- Dual-mode support: prefers-color-scheme + data-theme override
- Smooth theme transitions (150ms cubic-bezier)
- All semantic colors respond to theme changes
**Mobile Responsiveness:**
- Sidebar: Fixed overlay on mobile (<768px)
- Header: Responsive user menu collapse
- Footer: Multi-column → single column layout
- Touch-friendly icon buttons (40px minimum)
- Breadcrumb: Hidden on mobile to save space
**Accessibility:**
- ARIA labels on all interactive elements
- Skip navigation link
- Semantic HTML (nav, main, footer, header)
- Keyboard navigation support (ESC to close menus)
- Focus management in user dropdown
**Testing:**
- All 3 pages: ✅ 100% PASS (36/36 selectors)
- Layout integration verified
- Theme switching functional
- Mobile layout tested
**Commits:** Phase 1-3 now complete: 2681 LOC across 11 files
Next Phase: Phase 4 — Accessibility & Performance (2-4h)
- Complete ARIA + semantic HTML audit
- Keyboard navigation for data grids
- Performance optimization (lazy loading, code splitting)
- E2E accessibility testing
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
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