Add tests and implement functionality for staged cascade search and LSP expansion

- Introduced a new JSON file for verbose output of the Codex Lens search results.
- Added unit tests for binary search functionality in `test_stage1_binary_search_uses_chunk_lines.py`.
- Implemented regression tests for staged cascade Stage 2 expansion depth in `test_staged_cascade_lsp_depth.py`.
- Created unit tests for staged cascade Stage 2 realtime LSP graph expansion in `test_staged_cascade_realtime_lsp.py`.
- Enhanced the ChainSearchEngine to respect configuration settings for staged LSP depth and improve search accuracy.

ccw/frontend/src/lib/unsplash.ts

@@ -59,7 +59,7 @@ export async function searchUnsplash(
 export async function uploadBackgroundImage(file: File): Promise<{ url: string; filename: string }> {
   const headers: Record<string, string> = {
     'Content-Type': file.type,
-    'X-Filename': file.name,
+    'X-Filename': encodeURIComponent(file.name),
   };
   const csrfToken = getCsrfToken();
   if (csrfToken) {