feat: replace hardcoded orange hex values with blue equivalents

BrandLogo gradient, EmptyStateIllustrations SVGs, categoryColors,
landing page, brand SVG assets, and all remaining files.
Warning #eab308 → #fbbf24 (amber). categoryColors deduped.

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

frontend/src/components/dashboard/PerformanceCards.tsx

@@ -45,7 +45,7 @@ export function PerformanceCards() {
       label: 'Avg Resolution',
       value: avgMttr > 0 ? `${avgMttr}m` : '\u2014',
       icon: Clock,
-      iconColor: '#f97316',
+      iconColor: '#60a5fa',
       href: '/analytics',
     },
     {
@@ -59,7 +59,7 @@ export function PerformanceCards() {
       label: 'Session Time',
       value: totalMinutes > 0 ? `${totalMinutes}m` : '\u2014',
       icon: Timer,
-      iconColor: '#eab308',
+      iconColor: '#fbbf24',
       href: '/analytics',
     },
   ]