chore(tui): /clean recent perf work — KISS/DRY pass

24 files, -319 LoC. Behaviour preserved, 369/369 tests green.

- hermes-ink caches: shared lruEvict helper for the four parallel LRU
  caches (stringWidth, wrapText, sliceAnsi, lineWidth); touch-on-read
  stays inlined per cache; tightened output.ts skip-slice fast path.
- wheelAccel: trimmed provenance header, collapsed env parsing, ternary
  dispatch in computeWheelStep.
- perfPane: folded ensureLogDir into once-flag, spread-with-overrides
  for fastPath/phases instead of full rebuilds.
- env: extracted truthy() (used 4×).
- virtualHeights: collapsed user/diff/slash height bumps; trail+todos
  estimate.
- useInputHandlers: scrollIdleTimer cleanup on unmount, ?? undefined
  shorthand.
- useMainApp: dropped dead liveTailVisible IIFE and liveProgress
  indirection.
- appLayout, markdown, messageLine, entry: vertical rhythm, dropped
  narration comments, inlined one-shot vars.
- fix: empty catch blocks → /* best-effort */ for no-empty lint.

ui-tui/packages/hermes-ink/src/ink/stringWidth.ts

@@ -4,6 +4,8 @@ import stripAnsi from 'strip-ansi'
 
 import { getGraphemeSegmenter } from '../utils/intl.js'
 
+import { lruEvict } from './lru.js'
+
 const EMOJI_REGEX = emojiRegex()
 
 /**
@@ -299,6 +301,7 @@ export const stringWidth: (str: string) => number = str => {
 
       if (code >= 127 || code === 0x1b) {
         asciiOnly = false
+
         break
       }
     }
@@ -334,14 +337,5 @@ export function widthCacheSize(): number {
 }
 
 export function evictWidthCache(keepRatio = 0): void {
-  if (keepRatio <= 0) {
-    widthCache.clear()
-    return
-  }
-
-  const target = Math.floor(widthCache.size * keepRatio)
-
-  while (widthCache.size > target) {
-    widthCache.delete(widthCache.keys().next().value!)
-  }
+  lruEvict(widthCache, keepRatio)
 }