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/shared/IssueCard.tsx

@@ -177,7 +177,7 @@ export function IssueCard({
         onClick={handleClick}
         className={cn(
           'p-3 bg-card border border-border rounded-lg cursor-pointer',
-          'hover:shadow-md hover:border-primary/50 transition-all',
+          'hover:shadow-md hover:border-primary/50 transition-all hover-glow',
           className
         )}
       >
@@ -198,7 +198,7 @@ export function IssueCard({
       {...draggableProps}
       onClick={handleClick}
       className={cn(
-        'p-4 cursor-pointer hover:shadow-md hover:border-primary/50 transition-all',
+        'p-4 cursor-pointer hover:shadow-md hover:border-primary/50 transition-all hover-glow',
         className
       )}
     >