fix: wire export shortcut, text tool canvas integration, and undo rendering

1. Export dialog (Ctrl+Shift+S): replaced react-hotkeys-hook handler with
   a capture-phase keydown listener on window so the browser's native
   "Save Page As" dialog is intercepted before it can fire.

2. Text tool: created useTextTool hook that spawns an inline textarea
   overlay on canvas click, commits the text as a Konva Text object on
   blur/Enter, and wired it into the useActiveToolHandlers dispatcher.

3. Undo (Ctrl+Z): removed the 500ms debounce from zundo's handleSet.
   The debounce caused a race where calling undo before the timer fired
   would discard the future-states stack, making undo appear to do
   nothing.  The equality function (keyed on _historyVersion) already
   prevents intermediate states from being recorded, so the debounce
   was redundant.

apps/web/src/stores/editor-store.ts

@@ -732,14 +732,11 @@ export const useEditorStore = create<EditorState>()(
       equality: (a, b) =>
         (a as { _historyVersion: number })._historyVersion ===
         (b as { _historyVersion: number })._historyVersion,
-      // Issue #1: Forward all arguments from zundo's internal _handleSet
-      handleSet: (handleSet) => {
-        let timeout: ReturnType<typeof setTimeout>;
-        return (...args: Parameters<typeof handleSet>) => {
-          clearTimeout(timeout);
-          timeout = setTimeout(() => handleSet(...args), 500);
-        };
-      },
+      // Issue #1: Forward all arguments from zundo's internal _handleSet.
+      // No debounce -- the equality function (based on _historyVersion) already
+      // prevents intermediate states from being recorded.  Debouncing caused
+      // undo/redo to race with the delayed recording and silently discard the
+      // future-states stack.
     },
   ),
 );