feat(ui): numbered context-panel surface switching with configurable prefix

- Add switch_context_surface shortcut (default Cmd/Ctrl + 1..9, 0 for the 10th
  surface) that opens/closes/switches context panel rail surfaces by their
  visible order, configurable and persisted in Settings -> Shortcuts.
- Show order-number badges on rail icons while the modifier is held >500ms;
  dismiss on release, blur, or a number press until the next press-and-hold.
- Remove the legacy mod+2/3/4 (diff/terminal/git) and switch_tab_1..9 bindings
  so numbered surface switching goes only through the new mechanism.
- Replace the help-dialog 'Switch Project' row with the surface-switch row and
  update the shortcuts footer/header icons to the command icon.

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

@@ -1689,7 +1689,7 @@ export const dict: Record<I18nKey, string> = {
   "helpDialog.item.toggleTerminalExpanded": "Expandir o contraer terminal",
   "helpDialog.item.togglePlanContextPanel": "Alternar panel de contexto del plan",
   "helpDialog.item.cycleTheme": "Cambiar tema (Claro → Oscuro → Sistema)",
-  "helpDialog.item.switchProject": "Cambiar proyecto",
+  "helpDialog.item.switchContextSurface": "Cambiar superficie del panel de contexto (tecla numérica)",
   "helpDialog.item.toggleServicesMenu": "Mostrar u ocultar menú de servicios",
   "helpDialog.item.cycleServicesTab": "Cambiar pestaña de servicios",
   "helpDialog.item.openSettings": "Abrir configuración",