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/stores/useUIStore.ts

@@ -2412,7 +2412,7 @@ export const useUIStore = create<UIStore>()(
       {
         name: 'ui-store',
         storage: createDeferredSafeJSONStorage(),
-        version: 17,
+        version: 18,
         migrate: (persistedState, version) => {
           if (!persistedState || typeof persistedState !== 'object') {
             return persistedState;
@@ -2433,6 +2433,15 @@ export const useUIStore = create<UIStore>()(
             delete state.expandedEditorToolbar;
           }
 
+          // v17 -> v18: the default shortcut layout was redesigned around the
+          // mod+k leader and the held digit prefixes. Old overrides were
+          // recorded against the previous defaults (e.g. a bare 'mod' surface
+          // prefix now collides with session tabs), so custom bindings start
+          // fresh on the new system.
+          if (version < 18) {
+            delete state.shortcutOverrides;
+          }
+
           // v13 -> v14: the separate 'preview' surface merged into 'browser'.
           // Stored preview tabs keep their URL and become browser tabs; their
           // id encodes the mode, so it is rebuilt rather than left dangling.