Replaces the first-character-glyph + negative-text-indent trick (which let a
wide emoji or a leading disclosure caret knock the icon out of column) with a
genuine icon cell.
terminal.js: row() / details() / detailsDiff() take an optional `icon` that
goes in a fixed-width `.row-glyph` element (inline-block, 1.4em). Details
summaries wrap their text in a `.summary-text` span; the disclosure caret
moves to `.summary-text::before` so it leads the text, not the icon — keeping
the icon in the shared column. terminal.css carries the cell + caret rules.
app.js passes the per-tool emoji as `icon` for the flat tool-use row and every
expandable tool summary (Write/Edit/send/ask/answer/bash) plus the 💭 thinking
row, instead of string-prefixing it. A details `🖥️` now lines up under a flat
row's `🧠` regardless of emoji width. Doc: terminal-rendering.md layout
contract updated. Closes#1844.
1c47bd4333