Upgrade to HTML-based widgets for improved rendering

We’ve upgraded ValidMind’s rendering engine to a new HTML-based system, ensuring interactive components are preserved when notebooks are saved.

Key improvements:

• Interactive charts remain fully functional after saving and reopening notebooks.
• Progress bars persist their state across notebook sessions.
• More reliable rendering with improved state management.

To disable interactive figures, set VALIDMIND_INTERACTIVE_FIGURES=false (default: enabled).