feat: implement ADR-053 design system across all frontend components

Create design-system.css with all ADR-053 tokens:
- CSS custom properties: colors, spacing, fonts, panel dimensions
- Typography scale classes (heading-xl through data-lg)
- Form control and button base styles
- Custom scrollbar, selection highlight, animations

Update all components to use design system tokens:
- Replace hardcoded colors with var(--bg-surface), var(--border), etc.
- Replace generic monospace with var(--font-mono) (JetBrains Mono)
- Replace system font stack with var(--font-sans) (Inter)
- Replace spacing values with var(--space-N) tokens
- StatusBadge: use var(--status-online/warning/error/info)
- Dashboard: add stat cards with data-lg class, use StatusBadge
- FlashFirmware: pulse animation on progress bar during writes
- Settings: default bind_address 127.0.0.1 (matches ADR-050)

Add status bar footer with "Powered by rUv", node count, server status.
Load Inter + JetBrains Mono from Google Fonts in index.html.
Update ADR-053 status from Proposed to Accepted.

Co-Authored-By: claude-flow <ruv@ruv.net>

docs/adr/ADR-053-ui-design-system.md

@@ -2,7 +2,7 @@
 
 | Field | Value |
 |-------|-------|
-| Status | Proposed |
+| Status | Accepted |
 | Date | 2026-03-06 |
 | Deciders | ruv |
 | Depends on | ADR-052 (Tauri Desktop Frontend) |