Standalone MHA Fixes

[stephenegriffin]

This pull request fixes some regressions in the standalone MHA page.

UI Rendering Improvements:

• Prevents duplicate rows in tables by checking for existing row IDs before adding new ones in Table.ts.
• Skips adding table headers if they already exist, avoiding duplicate <thead> elements in Table.ts.
• Ensures that the left arrow UI element is only added once by checking for its existence in Table.ts.
• Clears the UI state before rebuilding sections in the analyze function to avoid residual artifacts.
• Adds missing diagnostic-accordion-item-template to mha.html for rendering diagnostic group items