feat: add keyboard shortcut help modal triggered by ? key

src/App.tsx

@@ -8,6 +8,7 @@ import { BoardView } from "@/components/board/BoardView";
 import { CommandPalette } from "@/components/command-palette/CommandPalette";
 import { SettingsDialog } from "@/components/settings/SettingsDialog";
 import { ToastContainer } from "@/components/toast/ToastContainer";
+import { ShortcutHelpModal } from "@/components/shortcuts/ShortcutHelpModal";
 import { useKeyboardShortcuts } from "@/hooks/useKeyboardShortcuts";
 
 export default function App() {
@@ -16,6 +17,7 @@ export default function App() {
   const view = useAppStore((s) => s.view);
 
   const [settingsOpen, setSettingsOpen] = useState(false);
+  const [shortcutHelpOpen, setShortcutHelpOpen] = useState(false);
 
   useEffect(() => {
     init();
@@ -42,6 +44,16 @@ export default function App() {
     };
   }, []);
 
+  useEffect(() => {
+    function handleOpenShortcutHelp() {
+      setShortcutHelpOpen(true);
+    }
+    document.addEventListener("open-shortcut-help", handleOpenShortcutHelp);
+    return () => {
+      document.removeEventListener("open-shortcut-help", handleOpenShortcutHelp);
+    };
+  }, []);
+
   const handleOpenSettings = useCallback(() => {
     setSettingsOpen(true);
   }, []);
@@ -66,6 +78,7 @@ export default function App() {
       <CommandPalette onOpenSettings={handleOpenSettings} />
       <SettingsDialog open={settingsOpen} onOpenChange={setSettingsOpen} />
       <ToastContainer />
+      <ShortcutHelpModal open={shortcutHelpOpen} onOpenChange={setShortcutHelpOpen} />
     </>
   );
 }

src/components/shortcuts/ShortcutHelpModal.tsx

@@ -0,0 +1,67 @@
+import {
+  Dialog,
+  DialogContent,
+  DialogHeader,
+  DialogTitle,
+  DialogDescription,
+} from "@/components/ui/dialog";
+
+interface ShortcutHelpModalProps {
+  open: boolean;
+  onOpenChange: (open: boolean) => void;
+}
+
+const SHORTCUT_GROUPS = [
+  {
+    category: "Navigation",
+    shortcuts: [
+      { key: "Ctrl+K", description: "Open command palette" },
+      { key: "?", description: "Show keyboard shortcuts" },
+      { key: "Escape", description: "Close modal / cancel" },
+    ],
+  },
+  {
+    category: "Board",
+    shortcuts: [
+      { key: "Ctrl+Z", description: "Undo" },
+      { key: "Ctrl+Shift+Z", description: "Redo" },
+    ],
+  },
+];
+
+export function ShortcutHelpModal({ open, onOpenChange }: ShortcutHelpModalProps) {
+  return (
+    <Dialog open={open} onOpenChange={onOpenChange}>
+      <DialogContent className="bg-pylon-surface sm:max-w-md">
+        <DialogHeader>
+          <DialogTitle className="font-heading text-pylon-text">
+            Keyboard Shortcuts
+          </DialogTitle>
+          <DialogDescription className="text-pylon-text-secondary">
+            Quick reference for all keyboard shortcuts.
+          </DialogDescription>
+        </DialogHeader>
+
+        <div className="flex flex-col gap-4">
+          {SHORTCUT_GROUPS.map((group) => (
+            <div key={group.category}>
+              <h4 className="mb-2 font-mono text-xs font-semibold uppercase tracking-widest text-pylon-text-secondary">
+                {group.category}
+              </h4>
+              <div className="flex flex-col gap-1">
+                {group.shortcuts.map(({ key, description }) => (
+                  <div key={key} className="flex items-center justify-between py-1">
+                    <span className="text-sm text-pylon-text">{description}</span>
+                    <kbd className="rounded bg-pylon-column px-2 py-0.5 font-mono text-xs text-pylon-text-secondary">
+                      {key}
+                    </kbd>
+                  </div>
+                ))}
+              </div>
+            </div>
+          ))}
+        </div>
+      </DialogContent>
+    </Dialog>
+  );
+}

src/hooks/useKeyboardShortcuts.ts

@@ -41,6 +41,12 @@ export function useKeyboardShortcuts(): void {
         document.dispatchEvent(new CustomEvent("close-all-modals"));
         return;
       }
+
+      if (e.key === "?" || (e.shiftKey && e.key === "/")) {
+        e.preventDefault();
+        document.dispatchEvent(new CustomEvent("open-shortcut-help"));
+        return;
+      }
     }
 
     document.addEventListener("keydown", handleKeyDown);