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/pages/HelpPage.tsx

@@ -286,7 +286,7 @@ export function HelpPage() {
       </div>
 
       {/* Search Documentation CTA */}
-      <Card className="p-6 sm:p-8 bg-gradient-to-r from-primary/5 to-primary/10 border-primary/20">
+      <Card className="p-6 sm:p-8 bg-gradient-accent border-primary/20">
         <div className="flex flex-col sm:flex-row items-start sm:items-center gap-4 sm:justify-between">
           <div className="flex items-start gap-4 flex-1 min-w-0">
             <div className="p-3 rounded-lg bg-primary/20 flex-shrink-0">

ccw/frontend/src/pages/ProjectOverviewPage.tsx

@@ -235,7 +235,7 @@ export function ProjectOverviewPage() {
           {/* Header Row */}
           <div className="flex items-start justify-between mb-4 pb-3 border-b border-border">
             <div className="flex-1">
-              <h1 className="text-lg font-semibold text-foreground mb-1">
+              <h1 className="text-lg font-semibold text-foreground gradient-text mb-1">
                 {projectOverview.projectName}
               </h1>
               <p className="text-sm text-muted-foreground">