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/cache-eviction.ts

@@ -9,12 +9,12 @@
 // (not session-keyed), so cross-session sharing is normally beneficial —
 // only evict when memory tightens or when the user explicitly resets.
 
+import { evictSliceCache, sliceCacheSize } from '../utils/sliceAnsi.js'
+
 import { evictLineWidthCache, lineWidthCacheSize } from './line-width-cache.js'
 import { evictWidthCache, widthCacheSize } from './stringWidth.js'
 import { evictWrapCache, wrapCacheSize } from './wrap-text.js'
 
-import { evictSliceCache, sliceCacheSize } from '../utils/sliceAnsi.js'
-
 export interface InkCacheSizes {
   lineWidth: number
   slice: number