fix: update workflow references to .github/ and gitignore xcuserstate

Update AGENTS.md and docs/ci-cd-setup.md from .gitea/workflows to .github/workflows

Add *.xcuserstate to .gitignore

Remove tracked UserInterfaceState.xcuserstate from git (preserve on disk)

.gitignore

@@ -66,4 +66,7 @@ DerivedData/
 
 # XcodeGen generated — NOT in version control
 TabataGo.xcodeproj
-build/
+build/
+
+# Xcode user state
+*.xcuserstate