Fix white underline/strikethrough lines when text or background color is applied

[Copilot]

Underline and strikethrough decoration lines render white after applying text or background color, because document.execCommand('foreColor') wraps content inside <u>/<strike> — but CSS text-decoration-color resolves to currentColor of the decorating element, not its children. So <u> inherits the theme's fg color (white in dark mode) regardless of the inner <font> tag.

Root cause

<!-- execCommand produces this structure -->
<u><font color="#000000">text</font></u>
<!-- <u> still inherits white from theme → white underline -->

<!-- correct structure needed -->
<font color="#000000"><u>text</u></font>
<!-- <u> now inherits black from <font> → black underline ✓ -->

Changes

• src/actions/formatSelection.ts — After foreColor execCommand in the whole-thought case, normalizes the contentEditable HTML to move color tags (<font>, <span> with color/background-color) outside of decoration tags (<u>, <strike>). Fires a synthetic input event so the debounced thought-value update picks up the corrected HTML.

  Two private helpers added:

  • isColorElement(el) — identifies <font> or <span> with color/background-color
  • normalizeColoredDecoration(html) — walks decoration elements bottom-up, hoisting sole color-element children above the decoration wrapper

• src/e2e/puppeteer/__tests__/color.ts — Three new tests asserting the correct HTML structure after: underline + text color, underline + background color, strikethrough + text color.

Only normalizes when the decoration element has exactly one child that is a color element (covers the whole-thought color application path). Partial-selection cases with multiple color spans are out of scope.

[raineorshine]

• Wait for Add "Worker Bee" agent for autonomous CI-driven PR iteration #4048