refactor: replace cyan accent with ember orange across entire frontend

Swap accent color from cyan (#22d3ee) to ember orange (#f97316) site-wide.
Cyan caused contrast issues and felt generic — orange brings warmth and
urgency fitting for a troubleshooting tool.

Changes:
- CSS variables: accent, accent-hover, accent-dim, accent-text, primary, ring
- Warning color shifted from amber (#fbbf24) to yellow (#eab308) for
  semantic separation from orange accent
- Brand SVGs: logo gradient updated to orange
- 50+ component files: all hardcoded cyan hex values, Tailwind cyan-*
  classes, and rgba(34,211,238,...) glow values replaced
- landing.css: all 45+ cyan references + 5 old border color fixes
- DESIGN-SYSTEM.md bumped to v5 with decisions log
- CLAUDE.md: all color references synced to charcoal palette + orange accent
- PWA theme-color meta tag updated to match sidebar (#10121a)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/layout/TopBar.tsx

@@ -126,7 +126,7 @@ export function TopBar() {
             <button
               onClick={() => setUserMenuOpen(!userMenuOpen)}
               className="flex h-8 w-8 items-center justify-center rounded-[10px] text-xs font-heading font-bold text-white hover:opacity-90 transition-opacity"
-              style={{ background: 'linear-gradient(135deg, #06b6d4, #22d3ee)' }}
+              style={{ background: 'linear-gradient(135deg, #ea580c, #f97316)' }}
               title={user?.name || user?.email || 'User'}
             >
               {initials}