feat(seo): add school name to URLs, fix sticky nav, collapse compare widget

- URLs now /school/138267-school-name instead of /school/138267
- Bare URN URLs redirect to canonical slug (backward compat)
- Remove overflow-x:hidden that broke sticky tab nav on secondary pages
- ComparisonToast starts collapsed — user must click to open

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nextjs-app/components/ComparisonToast.tsx

@@ -9,7 +9,7 @@ import styles from './ComparisonToast.module.css';
 export function ComparisonToast() {
   const { selectedSchools, clearAll, removeSchool } = useComparison();
   const [mounted, setMounted] = useState(false);
-  const [collapsed, setCollapsed] = useState(false);
+  const [collapsed, setCollapsed] = useState(true);
   const pathname = usePathname();
 
   useEffect(() => {