fix(tui): address Copilot review comments

- stringWidth: true LRU on cache hit (touch-on-read via delete+set) so
  hot strings stay resident under long sessions; was insertion-order
  FIFO before
- virtualHeights: include todos, panel sections, and intro version in
  messageHeightKey so height-cache reuse correctly invalidates when
  todo content / panel sections change
- virtualHeights: estimate trail+todos rows at todos.length+2 (or 2
  collapsed) instead of the generic ~1-line fallback, so initial
  virtualization offsets are closer to reality
- useInputHandlers: clearTimeout on unmount for scrollIdleTimer so
  pending relaxStreaming() never fires after teardown
- render-node-to-output: drop unused declined.noHint counter from
  scrollFastPathStats; it was always 0 (the "hint missing" branch is
  outside the diagnostics block)
- perfPane / hermes-ink.d.ts: follow the noHint removal
- wheelAccel: replace ~/claude-code path comment with generic
  attribution that doesn't reference a developer-local checkout

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

@@ -311,13 +311,16 @@ export const stringWidth: (str: string) => number = str => {
   const cached = widthCache.get(str)
 
   if (cached !== undefined) {
+    // True LRU: refresh recency by re-inserting (Map iteration is insertion order).
+    widthCache.delete(str)
+    widthCache.set(str, cached)
+
     return cached
   }
 
   const w = rawStringWidth(str)
 
   if (widthCache.size >= WIDTH_CACHE_LIMIT) {
-    // Drop oldest entry — Map iteration order is insertion order.
     widthCache.delete(widthCache.keys().next().value!)
   }