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/ink.tsx

@@ -979,15 +979,13 @@ export default class Ink {
     }
 
     const tWrite = performance.now()
+
     // Capture any stale pending write BEFORE starting this frame's write —
     // if the callback already fired, pendingWriteStart is null and lastDrainMs
     // already reflects the previous frame's drain.  If it hasn't fired, we
     // report "still pending" via a non-zero duration based on now-then so
     // backpressure shows up even if Node never flushes this session.
-    const staleDrain =
-      this.pendingWriteStart !== null
-        ? performance.now() - this.pendingWriteStart
-        : this.lastDrainMs
+    const staleDrain = this.pendingWriteStart !== null ? performance.now() - this.pendingWriteStart : this.lastDrainMs
 
     const prevFrameDrainMs = Math.round(staleDrain * 100) / 100
     this.lastDrainMs = 0
@@ -1016,6 +1014,7 @@ export default class Ink {
           }
         : undefined
     )
+
     const writeMs = performance.now() - tWrite
 
     // Update blit safety for the NEXT frame. The frame just rendered