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/shortcuts.ts

@@ -172,6 +172,13 @@ const SHORTCUT_ACTIONS: ReadonlyArray<ShortcutAction> = [
     description: 'Search and navigate within current conversation',
     customizable: true,
   },
+  {
+    id: 'toggle_prompt_navigator',
+    defaultCombo: 'mod+alt+p',
+    label: 'Toggle prompt navigator',
+    description: 'Show or hide the prompt navigator panel in chat',
+    customizable: true,
+  },
   {
     id: 'toggle_right_sidebar',
     defaultCombo: 'mod+b',