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/account/NotificationSettings.tsx

@@ -294,7 +294,7 @@ export function NotificationSettings() {
                           type="checkbox"
                           checked={config.events_enabled[eventKey] ?? false}
                           onChange={() => handleToggleEvent(config, eventKey)}
-                          className="h-3.5 w-3.5 rounded border-border bg-card text-primary focus:ring-primary/30 focus:ring-offset-0 cursor-pointer accent-[#06b6d4]"
+                          className="h-3.5 w-3.5 rounded border-border bg-card text-primary focus:ring-primary/30 focus:ring-offset-0 cursor-pointer accent-[#ea580c]"
                         />
                         <span className="text-sm text-foreground">{eventLabel}</span>
                       </label>