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/App.tsx

@@ -8,6 +8,7 @@ import {
   IconButton,
   Icons,
   StatTile,
+  UndoBar,
   usePersistedState,
 } from "./components";
 import { CommandPalette } from "./CommandPalette";
@@ -133,6 +134,12 @@ function segmentFill(stages: IngestStageInfo[], index: number, overallPercent: n
   return ((overallPercent - startPct) / (endPct - startPct)) * 100;
 }
 
+// How long the floating "Undo" snackbar stays up before auto-hiding itself.
+// This only controls the snackbar's visibility — the underlying undo action
+// stays available in the command palette well past this (see `undo` below),
+// so missing the snackbar isn't the last chance to undo.
+const UNDO_SNACKBAR_MS = 8000;
+
 export default function App() {
   const [status, setStatus] = useState<Status | null>(null);
   const [libStats, setLibStats] = useState<LibraryStats | null>(null);
@@ -140,6 +147,44 @@ export default function App() {
   const [progress, setProgress] = useState<IngestProgress | null>(null);
   const [busy, setBusy] = useState(false);
   const lastProgress = useRef<IngestProgress | null>(null);
+  // Lives here (not in LibraryBrowser) so it's reachable from the command
+  // palette, which is mounted at the app level and outlives any one tab's
+  // view across tab switches. Unlike the snackbar, this has no timeout —
+  // it's only replaced by a newer undo offer, run, or explicitly dismissed —
+  // so an undo that's missed in the snackbar is still reachable via Alt+/.
+  const [undo, setUndo] = useState<{ message: string; run: () => void | Promise<void> } | null>(
+    null,
+  );
+  const [snackbarVisible, setSnackbarVisible] = useState(false);
+  const snackbarTimer = useRef<ReturnType<typeof setTimeout> | null>(null);
+  // Bumped once an undo actually runs, so views mounted elsewhere than where
+  // the undo was offered (e.g. the Decks tab, when the undo came from a
+  // Library bulk add-to-deck) know to refetch instead of showing stale data
+  // until the user leaves and comes back.
+  const [deckRefreshSignal, setDeckRefreshSignal] = useState(0);
+
+  function offerUndo(message: string, run: () => void | Promise<void>) {
+    if (snackbarTimer.current) clearTimeout(snackbarTimer.current);
+    setUndo({ message, run });
+    setSnackbarVisible(true);
+    snackbarTimer.current = setTimeout(() => setSnackbarVisible(false), UNDO_SNACKBAR_MS);
+  }
+
+  // Explicit "×" on the snackbar: reject the whole offer, not just hide it.
+  function dismissUndo() {
+    if (snackbarTimer.current) clearTimeout(snackbarTimer.current);
+    setSnackbarVisible(false);
+    setUndo(null);
+  }
+
+  function runUndo() {
+    if (!undo) return;
+    const { run } = undo;
+    if (snackbarTimer.current) clearTimeout(snackbarTimer.current);
+    setSnackbarVisible(false);
+    setUndo(null);
+    Promise.resolve(run()).then(() => setDeckRefreshSignal((v) => v + 1));
+  }
 
   const refreshStatus = useCallback(async () => {
     setStatus(await api.getStatus());
@@ -393,18 +438,23 @@ export default function App() {
             ) : tab === "add" ? (
               <CardEntry />
             ) : tab === "library" ? (
-              <LibraryBrowser />
+              <LibraryBrowser onOfferUndo={offerUndo} />
             ) : (
-              <DeckView />
+              <DeckView refreshSignal={deckRefreshSignal} />
             )}
           </div>
         </div>
       </div>
+      {undo && snackbarVisible && (
+        <UndoBar message={undo.message} onUndo={runUndo} onDismiss={dismissUndo} />
+      )}
       <CommandPalette
         onNavigate={setTab}
         onUpdateCardData={updateCardData}
         onOpenLibrary={openLibrary}
         onNewLibrary={newLibrary}
+        undo={undo}
+        onRunUndo={runUndo}
       />
     </HoverPreviewProvider>
   );