Moodboard: move page-height class into Moodboard root

Every other tab applies its `h-[calc(100vh-56px)]` on its own root div;
the PageEditor wrappers stay bare. Moodboard was the outlier — wrapper
had `w-screen` + inline height of `calc(100vh - 68px)` (wrong 68px,
causing a 12px gap at the bottom). Move the class into `Moodboard.tsx`'s
root and drop the wrapper styling so it matches the rest.

frontend/apps/artcraft/app/src/pages/PageEnigma/PageEditor.tsx

@@ -650,10 +650,7 @@ export const PageEditor = () => {
         </div>
       )}
       {tabStore.activeTabId == "MOODBOARD" && moodboardPageEnabled && (
-        <div
-          className="w-screen"
-          style={{ height: "calc(100vh - 68px)" }}
-        >
+        <div>
           <Moodboard />
         </div>
       )}

frontend/apps/artcraft/app/src/pages/PageMoodboard/Moodboard.tsx

@@ -45,7 +45,7 @@ export const Moodboard = () => {
   }, [deleteSelected, setSelection, editingTextId]);
 
   return (
-    <div className="flex h-full w-full flex-col bg-[#0b0b0e]">
+    <div className="flex h-[calc(100vh-56px)] w-screen flex-col bg-[#0b0b0e]">
       <MoodboardToolbar />
       <div ref={containerRef} className="relative flex-1 overflow-hidden">
         <MoodboardStage containerRef={containerRef} stageRef={stageRef} />