feat(chat): desktop prompt navigator rail (#2054)

* feat(chat): add desktop prompt navigator rail

Add a ChatGPT-style right-center prompt marker rail for web/desktop chat
with hover/keyboard preview panel, load-more for partial history (panel only),
Chat setting, and mod+alt+p shortcut. Disabled in VS Code across rail,
shortcut, settings, help, and search surfaces.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* fix(ui): read promptNavigatorEnabled from getState in shortcut handler

Match the file convention used by other shortcut handlers so the toggle
does not rely on a hook-level selector closure.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* fix(ui): drop use-no-memo and default prompt navigator off

Remove the project-unprecedented React Compiler opt-out, and ship the
prompt navigator as opt-in to match other recent chat UI toggles.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

---------

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/lib/settings/search.ts

@@ -224,6 +224,13 @@ const SETTINGS_SEARCH_ITEMS: readonly SettingsSearchItem[] = [
     titleKey: 'settings.openchamber.visual.field.stickyUserHeader',
     keywords: ['messages', 'header'],
   },
+  {
+    id: 'chat.prompt-navigator',
+    page: 'chat',
+    titleKey: 'settings.openchamber.visual.field.promptNavigatorEnabled',
+    keywords: ['prompt', 'navigator', 'navigation', 'timeline', 'scroll'],
+    isAvailable: (ctx) => !ctx.isVSCode,
+  },
   {
     id: 'chat.collapsible-user-messages',
     page: 'chat',