feat(ui): add keyboard shortcut cheatsheet dialog on ? keypress

Shows a beautiful categorized cheatsheet of all keyboard shortcuts
(inbox, issue detail, global) when the user presses ? with keyboard
shortcuts enabled. Respects text input focus detection — won't trigger
in text fields. Uses the existing Dialog component and Radix UI.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/hooks/useKeyboardShortcuts.ts

@@ -6,6 +6,7 @@ interface ShortcutHandlers {
   onNewIssue?: () => void;
   onToggleSidebar?: () => void;
   onTogglePanel?: () => void;
+  onShowShortcuts?: () => void;
 }
 
 export function useKeyboardShortcuts({
@@ -13,6 +14,7 @@ export function useKeyboardShortcuts({
   onNewIssue,
   onToggleSidebar,
   onTogglePanel,
+  onShowShortcuts,
 }: ShortcutHandlers) {
   useEffect(() => {
     if (!enabled) return;
@@ -23,6 +25,13 @@ export function useKeyboardShortcuts({
         return;
       }
 
+      // ? → Show keyboard shortcuts cheatsheet
+      if (e.key === "?" && !e.metaKey && !e.ctrlKey && !e.altKey) {
+        e.preventDefault();
+        onShowShortcuts?.();
+        return;
+      }
+
       // C → New Issue
       if (e.key === "c" && !e.metaKey && !e.ctrlKey && !e.altKey) {
         e.preventDefault();
@@ -44,5 +53,5 @@ export function useKeyboardShortcuts({
 
     document.addEventListener("keydown", handleKeyDown);
     return () => document.removeEventListener("keydown", handleKeyDown);
-  }, [enabled, onNewIssue, onToggleSidebar, onTogglePanel]);
+  }, [enabled, onNewIssue, onToggleSidebar, onTogglePanel, onShowShortcuts]);
 }