Fix assistant.jpg: remove from LFS/XET and commit as regular file

- Remove duplicate and conflicting LFS/XET entries from .gitattributes
- Commit assistant.jpg as regular binary file (111 KB)
- Add .idea to .gitignore

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.gitignore

@@ -39,3 +39,5 @@ yarn-error.log*
 # typescript
 *.tsbuildinfo
 next-env.d.ts
+
+.idea