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/library/FolderEditModal.tsx

@@ -12,8 +12,8 @@ const FOLDER_COLORS = [
   '#8b5cf6', // Violet
   '#ec4899', // Pink
   '#ef4444', // Red
-  '#f97316', // Orange
-  '#eab308', // Yellow
+  '#60a5fa', // Orange
+  '#fbbf24', // Yellow
   '#22c55e', // Green
   '#14b8a6', // Teal
   '#3b82f6', // Blue