Add central layout.tsx for /learn/* and /parent/* routes

Next.js route-level layouts provide Sidebar + gradient background
automatically for all sub-pages. Individual pages no longer need
their own wrapper divs or Sidebar imports.

- learn/layout.tsx: Sidebar + purple gradient for all learning pages
- parent/layout.tsx: Same for all parent portal pages
- LearnLayout.tsx: Reusable component for other pages
- Fixed broken <LearnLayout>}> artifacts from previous refactoring
- Removed duplicate Sidebar/wrapper code from 9 sub-pages

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

studio-v2/app/learn/layout.tsx

@@ -0,0 +1,28 @@
+'use client'
+
+import { Sidebar } from '@/components/Sidebar'
+import { useTheme } from '@/lib/ThemeContext'
+
+/**
+ * Shared layout for ALL /learn/* pages.
+ * Provides: Sidebar + gradient background + flex container.
+ * Individual pages only need to render their content.
+ */
+export default function LearnLayout({ children }: { children: React.ReactNode }) {
+  const { isDark } = useTheme()
+
+  return (
+    <div className={`min-h-screen flex relative overflow-hidden ${
+      isDark
+        ? 'bg-gradient-to-br from-indigo-900 via-purple-900 to-pink-800'
+        : 'bg-gradient-to-br from-slate-100 via-blue-50 to-cyan-100'
+    }`}>
+      <div className="relative z-10 p-4 flex-shrink-0">
+        <Sidebar />
+      </div>
+      <div className="flex-1 flex flex-col relative z-10 overflow-y-auto">
+        {children}
+      </div>
+    </div>
+  )
+}