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/src/lib/memoryMonitor.ts

@@ -41,10 +41,8 @@ export function startMemoryMonitor({
       return
     }
 
-    // Defensive eviction: prune Ink content caches before dumping/exiting.
-    // 'high' = half-prune (still warm enough to recover quickly);
-    // 'critical' = full drop. Reduces post-dump RSS and gives the user a
-    // chance to keep running rather than auto-restart.
+    // Prune Ink content caches before dump/exit — half on 'high' (recoverable),
+    // full on 'critical' (post-dump RSS reduction, keeps user running).
     evictInkCaches(level === 'critical' ? 'all' : 'half')
 
     dumped.add(level)