Ignore Xcode shared scheme data

Auto-generated by Xcode/xcodebuild when no shared scheme exists yet;
not meant to be tracked.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -4,6 +4,7 @@
 
 ## User settings
 xcuserdata/
+xcshareddata/
 
 ## compatibility with Xcode 8 and earlier (ignoring not required starting Xcode 9)
 *.xcscmblueprint