feat(settings): add streaming auto-follow toggle

New Streaming section on the Chat settings page with a checkbox that
controls whether the viewport follows new content while a response
streams. Default stays on. With it off, the anchored user message still
parks at the top on send, but no glide or end-follow correction runs and
the list's maintain-scroll-at-end stays disabled; the scroll-to-bottom
pill and session open keep scrolling explicitly.

Persisted through desktop settings like the other chat toggles (auto-save
diff, authoritative apply, sanitize), registered in settings search, and
localized in every locale.

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

@@ -1939,6 +1939,10 @@ export const settingsDict = {
   'settings.openchamber.visual.section.showToolsOpenedByDefault': 'デフォルトで開くツールを表示',
   'settings.openchamber.visual.section.sessionAssistance': 'セッション支援',
   'settings.openchamber.visual.section.reasoning': '推論',
+  'settings.openchamber.visual.section.streaming': 'ストリーミング',
+  'settings.openchamber.visual.field.streamingAutoFollow': '応答のストリーミング中に新しい内容を追従',
+  'settings.openchamber.visual.field.streamingAutoFollowAria': '応答のストリーミング中に新しい内容へ自動スクロールする',
+  'settings.openchamber.visual.field.streamingAutoFollowInfo': '応答の受信中、ビューは常に最新の内容へスクロールします。オフにするとビューは動かず、手動でスクロールできます。',
   'settings.openchamber.visual.section.messageAppearance': 'メッセージの外観',
   'settings.openchamber.visual.section.toolsAndFiles': 'ツールとファイル',
   'settings.openchamber.visual.section.composer': '入力欄',