perf(native): smoother scrolling on Rune, less work per frame, code block line breaks - #480

🟢 Confidence 9/10 · safe to merge. The delta is one constant in a bench script; the remaining gap is the untested kept-row path in containerRows (earlier finding F1).
_{1 note · tests partial −1 · risk medium}

Only the bench harness changed since the last review: the sidebar channel-menu check now hovers a channel row at [200, 270] so the row's dots trigger is showing when clickLabel presses it. No new defects in that hunk.

• sidebar channel menu check hovers [200, 270] instead of [200, 220], over a channel row

Still open from earlier reviews

• 🔵 Note · F1 · containerRows' kept rows are untested · apps/web-foldkit/src/mount/message-list.ts:837

_{8544251 · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}