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/sidebar/SidebarStatsBar.tsx

@@ -68,7 +68,7 @@ export function SidebarStatsBar({ resolved, active, completedMinutes, activeSess
       <div className="flex-1 rounded-md bg-[rgba(255,255,255,0.02)] px-1 py-1.5 text-center">
         <div
           className="font-mono text-sm font-semibold leading-none"
-          style={{ color: '#22d3ee' }}
+          style={{ color: '#f97316' }}
           aria-label={`${active} active sessions`}
         >
           {active}