feat: add Unsplash search hook and API proxy routes

- Implemented `useUnsplashSearch` hook for searching Unsplash photos with debounce.
- Created Unsplash API client functions for searching photos and triggering downloads.
- Added proxy routes for Unsplash API to handle search requests and background image uploads.
- Introduced accessibility utilities for WCAG compliance checks and motion preference management.
- Developed theme sharing module for encoding and decoding theme configurations as base64url strings.

ccw/frontend/src/components/dashboard/DashboardHeader.tsx

@@ -43,7 +43,7 @@ export function DashboardHeader({
   return (
     <div className="flex items-center justify-between">
       <div>
-        <h1 className="text-2xl font-semibold text-foreground">
+        <h1 className="text-2xl font-semibold text-foreground gradient-text">
           {formatMessage({ id: titleKey })}
         </h1>
         <p className="text-sm text-muted-foreground mt-1">

ccw/frontend/src/components/dashboard/widgets/WorkflowTaskWidget.tsx

@@ -253,7 +253,7 @@ function WorkflowTaskWidgetComponent({ className }: WorkflowTaskWidgetProps) {
   return (
     <div className={cn('flex flex-col gap-2', className)}>
       {/* Project Info Banner - Separate Card */}
-      <Card className="shrink-0">
+      <Card className="shrink-0 border-gradient-brand">
         {projectLoading ? (
           <div className="px-4 py-3 flex items-center gap-4">
             <div className="h-5 w-32 bg-muted rounded animate-pulse" />