fix: adapt frontend image paths for backend port 8002 and use blob download

Backend port changed from 8000 to 8002 due to port conflict (frpc on Windows).
- Add resolveImageUrl() to convert relative image URLs to full backend URLs
- Fix all spatial page image src and download handlers to use backend address
- Fix chat message image rendering to use correct port
- Switch download to blob-based approach to support cross-origin file saving

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitignore

@@ -71,3 +71,5 @@ Desktop.ini
 htmlcov/
 
 officefile
+data/1法律
+