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/line-width-cache.ts

@@ -1,3 +1,4 @@
+import { lruEvict } from './lru.js'
 import { stringWidth } from './stringWidth.js'
 
 // During streaming, text grows but completed lines are immutable.
@@ -13,6 +14,7 @@ export function lineWidth(line: string): number {
   if (cached !== undefined) {
     cache.delete(line)
     cache.set(line, cached)
+
     return cached
   }
 
@@ -32,14 +34,5 @@ export function lineWidthCacheSize(): number {
 }
 
 export function evictLineWidthCache(keepRatio = 0): void {
-  if (keepRatio <= 0) {
-    cache.clear()
-    return
-  }
-
-  const target = Math.floor(cache.size * keepRatio)
-
-  while (cache.size > target) {
-    cache.delete(cache.keys().next().value!)
-  }
+  lruEvict(cache, keepRatio)
 }