Add deck synergy suggestions, a responsive deck layout, and undoable library bulk-add

Suggestion scoring is fully offline (tribal/mechanic/archetype/mana-base
signals derived at ingest, no external synergy database), with an "unusual
picks" mode that surfaces underappreciated cards instead of staples. The
deck page's top panels now use a CSS grid so wide windows don't waste
horizontal space. Library's bulk add-to-deck can clobber existing deck
quantities, so it now offers an undo (snackbar + command palette, the
latter with no timeout) that restores each card's prior state exactly.

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

src/CommandPalette.tsx

@@ -30,18 +30,25 @@ function subsequenceMatch(query: string, text: string): boolean {
  * Alt+/ opens a fuzzy-searchable palette of navigation commands, decks, and
  * cards. Selecting a deck switches to the Decks tab with it pre-selected;
  * selecting a card opens the existing click-to-zoom preview modal without
- * changing tabs.
+ * changing tabs. When an undoable action's grace window hasn't lapsed yet,
+ * an "Undo: …" entry is listed first, so Alt+/ then Enter is a fast way to
+ * undo without hunting for the floating snackbar's button.
  */
 export function CommandPalette({
   onNavigate,
   onUpdateCardData,
   onOpenLibrary,
   onNewLibrary,
+  undo,
+  onRunUndo,
 }: {
   onNavigate: (tab: Tab) => void;
   onUpdateCardData: () => void;
   onOpenLibrary: () => void;
   onNewLibrary: () => void;
+  /** The most recent undoable action, if its window hasn't lapsed yet. */
+  undo: { message: string; run: () => void | Promise<void> } | null;
+  onRunUndo: () => void;
 }) {
   const [open, setOpen] = useState(false);
   const [query, setQuery] = useState("");
@@ -83,6 +90,7 @@ export function CommandPalette({
   }
 
   const staticCommands: PaletteItem[] = [
+    ...(undo ? [{ key: "undo", label: `Undo: ${undo.message}`, run: onRunUndo }] : []),
     { key: "nav-add", label: "Go to Add Cards", run: () => onNavigate("add") },
     { key: "nav-library", label: "Go to Library", run: () => onNavigate("library") },
     { key: "nav-decks", label: "Go to Decks", run: () => onNavigate("decks") },