Ignore .derivedDataAgent and remove local build artifacts from disk

Agent builds used a workspace-local DerivedData path; ignore it like
other Xcode output. Deleted .derivedData, .derivedDataAgent, and build/
folders from the repo tree (regenerable).

Co-authored-by: Cursor <cursoragent@cursor.com>

.gitignore

@@ -2,6 +2,7 @@
 .DS_Store
 DerivedData/
 .derivedData/
+.derivedDataAgent/
 .derivedDataBuild/
 build/
 *.xcuserstate