fix: edit button styling and precise hit area

[osolmaz]

Summary

The edit affordance looked like a text link and, worse, clicking anywhere on its row triggered it.
It now renders exactly like the other buttons — accent background, [✏ edit] with an icon in the emoji symbol set — and only the label itself is clickable.

What Changed

• ContentRow targets gain an optional clickable width; button-like rows set it to their rendered label width, and hit-area registration clamps it to the viewport. List rows (links, settings) keep their full-row hit areas.
• The edit rows use the shared button_style and a new edit_button symbol ([✏ edit] emoji, [edit] ASCII).
• Wrapped fragments preserve the precise width, so degenerate ultra-narrow layouts cannot fall back to full-row clicks (review finding).

Testing

• cargo test: 691 pass, including new assertions that the hit area equals the label width, that a click beside the button does nothing while the label still opens the composer, and that the button carries the shared style.
• fmt/clippy -D warnings/slophammer clean; capture manifests re-stamped (unauthenticated fixtures render no edit buttons, so frames are unchanged).
• Codex review: the one finding (wrap fragments losing the width) is fixed.

Risks

Minimal — a rendering/hit-area change scoped to rows that opt into a precise width.

[osolmaz]

Final report: merged as ff8de35. Edit affordance now uses the shared button style with an icon ([✏ edit] / [edit] in ASCII) and a hit area covering exactly the label — clicking beside it does nothing. ContentRow gained an opt-in precise target width, preserved across wrapped fragments per the review finding. 691 tests green.