chore: add .idea/ to .gitignore

Add JetBrains IDE .idea/ directory to .gitignore to prevent
Rider and other JetBrains IDE configuration files from being
tracked in version control.

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

Author: JusterZhu

.gitignore

@@ -396,3 +396,6 @@ FodyWeavers.xsd
 
 # JetBrains Rider
 *.sln.iml
+
+# JetBrains IDEs (IntelliJ, Rider, etc.)
+.idea/