figma-transformer: emit inline character-level text styles (spans for mixed color/weight)

[chubes4]

Problem

Text nodes in Figma can have character-level style overrides — different fill colors, font weights, font sizes per character run. Currently the emitter applies only the outer text node style, so mixed-color text (e.g. one word blue, rest black) renders entirely in the outer color.

Example from FSE Pilot Build Theme: the heading "We're all about Lego" has the word "Lego" in blue (#0000ff or brand color), but the emitter outputs the entire heading as a single text node with one color.

How Figma encodes this

Text nodes carry:

• characters — the full string
• characterStyleOverrides — array of style-table IDs, one entry per character (0 = base style, N = override)
• styleOverrideTable — map from override ID to style object with fills, fontFamily, fontWeight, fontSize, fontStyle, etc.

Proposed fix

In StaticHtmlEmitter, when emitting a TEXT node:

1. Check if characterStyleOverrides is non-empty and has more than one distinct value
2. If so, split characters into runs by contiguous style ID
3. For each run, look up the override in styleOverrideTable and emit a <span> with inline color:, font-weight:, font-style: etc. where those override the base
4. Wrap all runs inside the outer element (h1, p, etc.)

When all characters share the same style (the common case), emit as today (no spans).

Impact

Color/weight emphasis within text nodes — a common pattern in marketing and editorial designs.