Admin: split long pages into tabs instead of scrolling; v2.9.2

- Shared tab bar; chosen tab is remembered per page
- Current Series: Main Series / Second Series / Launch: Main / Launch: Second
- Resources, Footer & Global, SEO, Legal, Start Here, Custom Links: former "Jump to" scroll links are now tabs
- Dashboard: Overview / Recent Activity / Study Users
- Studies editor: Lessons / Study Settings

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/App.css

@@ -13135,3 +13135,6 @@
   border-bottom: 1px solid rgba(201, 168, 76, 0.22);
   padding-bottom: 0.5rem;
 }
+
+.admin-tabs--page { margin: 0 0 1.5rem; padding-bottom: 1rem; border-bottom: 1px solid #2a2518; }
+.admin-tabs--page .admin-tab { font-size: 0.8rem; padding: 0.45rem 0.9rem; }