feat(ui): redesign the default shortcut layout around a mod+k leader

Single chords stay for everyday actions; open/go actions move to two-step
mod+k sequences; held mod+digit switches header session tabs and held
mod+alt+digit switches context panel surfaces. Rare actions leave the
shortcut schema for the command palette, every remaining action ships with
a default binding, and stored overrides from the old layout reset once.
Key matching now follows the physical key on non-Latin layouts and for
Option-modified digits on macOS, including in the recording dialog.

packages/ui/src/components/layout/Header.tsx

@@ -1471,17 +1471,6 @@ export const Header: React.FC = () => {
       setIsDesktopServicesOpen(true);
       void refreshCurrentInstanceLabel();
     },
-    // The desktop menu holds one destination now, so this shortcut opens it
-    // rather than cycling. The binding is kept: it is user-configurable and
-    // silently dropping it would break existing setups.
-    cycle_services_tab: () => {
-      if (servicesTabs.length === 0) return false;
-      setIsDesktopServicesOpen(true);
-      void refreshCurrentInstanceLabel();
-    },
-    toggle_context_plan: () => {
-      handleOpenContextPlan();
-    },
   });
 
   const desktopSidebarActions = (