feat(chat): migrate history list to @tanstack/react-virtual with deterministic mobile history loading

- Replace virtua with @tanstack/react-virtual for chat history on all
  surfaces: bottom anchoring (anchorTo: end), key-stable prepend
  preservation, and native iOS touch/momentum deferral live in the core
- Patch virtual-core to clamp the render range to real scroll bounds
  during transient adjustments
- Rows render in normal flow inside a translated wrapper so sticky user
  headers keep working; measurement snapshots cached per session
- Pre-write container height in scrollToFn so the browser cannot clamp
  anchor corrections to the stale height; hold the prepend anchor for up
  to 180 frames on mobile while fresh rows settle (cancelled by user
  input; desktop relies on core anchoring alone)
- Adaptive row-size estimate from per-session measured averages; disable
  reveal fade-in for virtualized history rows
- Mobile loads older history only through an explicit localized top
  button: no scroll-position trigger and no post-mount background
  prepend, so every insert happens from a resting state; a quiet-window
  hold defers any stray prepend commit while a touch gesture is active
- Desktop/VS Code keep the seamless scroll-up trigger and progressive
  background prepend

packages/ui/src/lib/i18n/messages/ja.ts

@@ -1284,6 +1284,7 @@ export const dict: Record<I18nKey, string> = {
   'diffView.hunk.discardTitle': 'ハンク{index}を破棄',
   'diffView.hunk.unavailable': 'このハンクはもう利用できません。差分を更新してからもう一度お試しください。',
   'diffView.hunk.unsupported': '個別のハンクのステージングはこのランタイムではサポートされていません。',
+  'chat.history.loadOlder': '以前のメッセージを読み込む',
   'chat.autoReview.title': 'コードレビューループが実行中です',
   'chat.autoReview.status.waitingForReviewer': 'レビュアーを待機中',
   'chat.autoReview.status.waitingForImplementer': '実装者を待機中',