fix(ui): emoji ZWJ sequences compose, and wrapping measures the font that draws

[tannevaled]

🧑‍🚀 drew as a person standing next to a rocket

The shaper was never the problem. go-opentype/shape composes the sequence correctly when handed it whole — I checked before changing anything: it returns exactly one glyph.

The damage happened before it was called. The toolkit's fallback routing split runs per rune, and the zero-width joiner is carried by several script faces — Thai, Arabic, Devanagari and Hebrew all ship U+200D for their own shaping. First-face-wins routing therefore handed the joiner to the Thai face, and the sequence reached the shaper as three runs: person, joiner, rocket. The GSUB ligature never saw them together.

Fixed in the owning library (go-widgets/toolkit#168, v0.127.0): a rune that continues the preceding grapheme stays in the current run whenever that run's face can render it. This PR bumps to it and asserts the result through the reader's own chain — 🧑‍🚀 and 👨‍👩‍👦 each measure exactly one glyph's advance.

Three wraps measured the wrong font

While verifying, three callers turned out to violate the rule wrapMeasured's own doc comment states: they wrapped with a textFace (the x/image measurer) but drew with a toolkit.Font. detailContent, previewContent and previewHeaderLines now wrap with the font that actually draws the line, as the feed card already did.

A line that "fits" one rasteriser can overflow the other and be clipped mid-word. Composed emoji widened the gap: a ZWJ sequence is two glyphs to the x/image measurer and one to the shaper that draws it.

wrapText is deleted rather than left as a trap — it defaulted to the textFace measurer, which is the wrong choice for every remaining caller, while wrapMeasured takes the measurer explicitly.

Verification

• go test -race over the gated packages → 100.0% of statements, race-clean.
• Proved on pixels: 🧑‍🚀 renders as a single helmeted face in a live @nasa card (it previously occupied two cells), and 👨‍👩‍👦, 👩‍💻, 👨‍🍳 compose too.

Second commit

style: gofmt ui/icons.go and ui/scene.go — both were already gofmt-unclean on main; a directory-wide gofmt while working next door picked them up. Split into its own commit so it does not hide inside a behaviour change. Alignment only, no code.

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