Add DOM instrumentation tags and harden VirtualItem visibility for hidden/zero-sized roots to prevent inactive instances from keeping heavy tool-call markup mounted; restore message stream virtualization margin.
Converts hardcoded UI copy to i18n keys across the app, adds global translation for non-component modules, and splits the English catalog into feature modules with duplicate-key detection.
- Add clipboard utility with fallback for non-secure contexts
- Implement modern Clipboard API with document.execCommand fallback
- Update copy buttons in code blocks, markdown, messages, and session list
- Add proper error handling and user feedback for copy operations
Fixes issue where copy buttons did not work in web browsers served over HTTP or without Clipboard API support
