157 : Make HTML Field theme-aware (light/dark support)

[lattln]

Summary

Improves the HTML Field iframe rendering so embedded HTML content properly follows the application’s light/dark theme. Previously, the iframe was isolated from parent styles and fell back to browser defaults.

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Key Changes

• Added theme-aware default styles for HTML content rendered inside iframes
• Reads semantic color CSS variables (--mie-color-*) from the parent editor/renderer root
• Injects those variables into the iframe :root so styles stay in sync
• Automatically updates when theme changes (via MutationObserver)

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Behavior

• Common HTML elements (p, headings, lists, tables, code, etc.) render with readable, theme-consistent styles
• Defaults apply only when user HTML has no explicit styles
• User-provided styles always take precedence
• Falls back to light mode if theme variables are not yet available

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Implementation Notes

• Uses getComputedStyle() to read actual resolved theme values
• Centralized theme constants and helpers for DRY/KISS compliance
• Removed unused state and dead code

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Files Changed

• HTML_Field.jsx

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Testing

• Verified HTML content updates live when toggling light/dark mode
• Confirmed custom inline and <style>-based user HTML is not overridden

Here’s a clean PR-ready section you can drop straight into the PR description under Testing or How to Test.
It’s concise, explicit, and reviewer-friendly.

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How to Test (Local Package Validation)

This change was validated using a local packed build of the package and installed into an external project to verify real-world behavior.

Steps:

1. From the questionnaire-builder repo:

   # which builds the packages and pack it locally for you insdie of ./localpackages/...
   npm run pack:local
   

2. Locate the generated tarball(s) in:

   localpackages/..
   

3. In the consuming project (e.g. bluehive-ai or another external app), install the local package:

   npm install /absolute/path/to/questionnaire-builder/localpackages/package/<package-name>.tgz

4. Start the consuming application and verify:

   • HTML Field renders with correct light/dark theming
   • Theme changes propagate live into iframe content
   • No regressions in other form fields
   • User-provided HTML styles still take precedence

Notes:

• This bypasses npm registry publishing and tests the package exactly as it would ship.
• Repeat install for editor/renderer/engine packages as needed.