feat(e10): a jump-to palette on Ctrl/Cmd+K

Reaching a channel three modules away cost a rail, a page and a scroll.
Now it costs a keystroke and half a word: Mod+K searches modules,
channels, playlists, the saved views applicable where you stand, and the
app-wide actions.

Scope agreed with the product owner: navigation + actions, but only the
reversible local ones (the shortcuts sheet, the theme). "Sync from
YouTube" is deliberately absent — it is a long-running job against a
quota, it wants the progress and error surface the Channels page already
gives it, and one mistyped Enter is a worse failure than the walk it
would have saved.

Matching is word-wise and accent-folded, because this is a bilingual app
and nobody reaches for the accent keys in a hurry: "pod thevr" finds
TheVR Podcast and "penzugy" finds pénzügy. The arrows walk one flat
result list so crossing a group heading is invisible, and the field
carries the combobox/listbox aria tree that virtual selection needs.

ui/CommandPalette is domain-free (items are a prop, per the ui/ import
rule); AppCommandPalette supplies them. The shell is Modal again, with a
new `top` placement so a search-first dialog grows downwards instead of
jumping as results change.

Also fixes a bug the palette hit on its first run, and that PlayerModal
had already hit once: closing a dialog reclaims its Back-to-close
history entry with a programmatic history.back(), which undoes any
pushState made before it lands — so a command that navigates only closed
the palette. The rule is now closeThenNavigate() in history.ts with a
test, and PlayerModal's inline copy is gone.

The global `h` moves out of KeyboardHelp into useGlobalKeymap beside
Mod+K, so one listener owns the whole `global` scope and dispatch's
exhaustiveness keeps meaning what it says.

frontend/src/App.tsx

@@ -35,6 +35,8 @@ import GlassTuner from "./components/GlassTuner";
 import ChatDock from "./components/ChatDock";
 import Toaster from "./components/ui/Toaster";
 import KeyboardHelp from "./components/ui/KeyboardHelp";
+import AppCommandPalette from "./components/AppCommandPalette";
+import { useGlobalKeymap } from "./lib/keymap";
 import { StateMessage } from "./components/ui/QueryState";
 import ErrorDialog from "./components/ErrorDialog";
 import VersionBanner from "./components/VersionBanner";
@@ -57,6 +59,9 @@ export default function App() {
   const { t, i18n } = useTranslation();
   const { page, channelView, ytSearch } = useNavigation();
   const { setPage, enterYtSearch } = useNavigationActions();
+  // The `global` key scope, bound once for the whole app: `h` opens the cheat sheet, Mod+K the
+  // jump-to palette (both rendered at the bottom of this tree).
+  useGlobalKeymap();
   // An emailed verification link is confirmed HERE, above the signed-in/signed-out branch below, so
   // it works in a browser that already holds a session. It used to be handled inside Welcome, which
   // that branch never renders when signed in — the token was silently dropped. Signed out, the
@@ -413,9 +418,11 @@ export default function App() {
             (collapsed or expanded) without tracking its width. */}
         <Toaster />
       </div>
-      {/* The app-wide keyboard cheat sheet + the global `h` that opens it. Mounted once, outside
-          the page area, so every surface answers "what can I press here" the same way. */}
+      {/* The two app-wide overlays: the keyboard cheat sheet (`h`) and the jump-to palette (Mod+K).
+          Mounted once, outside the page area, so every surface answers "what can I press here" and
+          "take me to X" the same way. Their keys are bound by useGlobalKeymap above. */}
       <KeyboardHelp />
+      <AppCommandPalette />
       {meQuery.data && !meQuery.data.is_demo && <ChatDock meId={meQuery.data.id} />}
       <Suspense fallback={null}>
         {aboutOpen && (