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/src/core/websocket.ts

@@ -164,6 +164,9 @@ export function handleWebSocketUpgrade(req: IncomingMessage, socket: Duplex, _he
   wsClients.add(socket);
   console.log(`[WS] Client connected (${wsClients.size} total)`);
 
+  // Replay any buffered A2UI surfaces to the new client
+  a2uiWebSocketHandler.replayPendingSurfaces(socket);
+
   // Handle incoming messages
   let pendingBuffer = Buffer.alloc(0);