Add deck legality checking, deck/library import-export, and a command palette

Threads Scryfall's per-format legalities through the reference db and adds a
deck-page indicator (structural rules + banned/restricted lists) that lists
violation reasons inline. Decks and selected library cards can now be
exported to/imported from plain-text decklists, with best-effort name
resolution and a report of anything that didn't match. Also adds a shuffle-
and-draw sample hand modal, and an Alt+/ command palette for jumping to a
tab, deck, or card without leaving the keyboard.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/App.tsx

@@ -10,6 +10,7 @@ import {
   StatTile,
   usePersistedState,
 } from "./components";
+import { CommandPalette } from "./CommandPalette";
 import { CardEntry } from "./views/CardEntry";
 import { LibraryBrowser } from "./views/LibraryBrowser";
 import { DeckView } from "./views/DeckView";
@@ -399,6 +400,12 @@ export default function App() {
           </div>
         </div>
       </div>
+      <CommandPalette
+        onNavigate={setTab}
+        onUpdateCardData={updateCardData}
+        onOpenLibrary={openLibrary}
+        onNewLibrary={newLibrary}
+      />
     </HoverPreviewProvider>
   );
 }