Drop the IntelliJ project files; ignore /.idea/ as a whole

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QLJfZQZeAKAwSqViTmLzki

.gitignore

@@ -1,12 +1,7 @@
 *.iml
 .gradle
 /local.properties
-/.idea/caches
-/.idea/libraries
-/.idea/modules.xml
-/.idea/workspace.xml
-/.idea/navEditor.xml
-/.idea/assetWizardSettings.xml
+/.idea/
 .DS_Store
 /build
 /captures