Move design configurables to right panel, hide shell right panel on design tab

- ProjectShell right panel (Discovery/Captured) hidden when on design tab
- SurfaceSection restructured: scaffold preview center, controls right panel (280px)
- Library cards in 2-col grid, configurator and color picker scroll in right panel
- Main content area uses full height without extra padding

Made-with: Cursor

components/layout/project-shell.tsx

@@ -239,15 +239,16 @@ export function ProjectShell({
           </div>
         </div>
 
-        {/* Right panel */}
+        {/* Right panel — hidden on design tab (design page has its own right panel) */}
         <div className="vibn-right-panel" style={{
-          width: 230,
-          borderLeft: "1px solid #e8e4dc",
+          width: activeTab === "design" ? 0 : 230,
+          borderLeft: activeTab === "design" ? "none" : "1px solid #e8e4dc",
           background: "#fff",
-          padding: "22px 18px",
+          padding: activeTab === "design" ? 0 : "22px 18px",
           overflow: "auto",
           flexShrink: 0,
           fontFamily: "Outfit, sans-serif",
+          display: activeTab === "design" ? "none" : undefined,
         }}>
           {/* Discovery phases */}
           <SectionLabel>Discovery</SectionLabel>