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/locales/en/codexlens.json

@@ -224,10 +224,26 @@
     "content": "Content Search",
     "files": "File Search",
     "symbol": "Symbol Search",
+    "semantic": "Semantic Search (LSP)",
     "mode": "Mode",
     "mode.semantic": "Semantic (default)",
     "mode.exact": "Exact (FTS)",
     "mode.fuzzy": "Fuzzy",
+    "semanticMode": "Search Mode",
+    "semanticMode.fusion": "Fusion Search",
+    "semanticMode.vector": "Vector Search",
+    "semanticMode.structural": "Structural Search",
+    "fusionStrategy": "Fusion Strategy",
+    "fusionStrategy.rrf": "RRF (default)",
+    "fusionStrategy.dense_rerank": "Dense Rerank",
+    "fusionStrategy.binary": "Binary",
+    "fusionStrategy.hybrid": "Hybrid",
+    "fusionStrategy.staged": "Staged",
+    "lspStatus": "LSP Status",
+    "lspAvailable": "Semantic search available",
+    "lspUnavailable": "Semantic search unavailable",
+    "lspNoVector": "Vector index required",
+    "lspNoSemantic": "Semantic dependencies required",
     "query": "Query",
     "queryPlaceholder": "Enter search query...",
     "button": "Search",