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/app/sitemap.ts

@@ -5,6 +5,7 @@
 
 import { MetadataRoute } from 'next';
 import { fetchSchools } from '@/lib/api';
+import { schoolUrl } from '@/lib/utils';
 
 const BASE_URL = 'https://schoolcompare.co.uk';
 
@@ -39,7 +40,7 @@ export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
     });
 
     const schoolPages: MetadataRoute.Sitemap = schoolsData.schools.map((school) => ({
-      url: `${BASE_URL}/school/${school.urn}`,
+      url: `${BASE_URL}${schoolUrl(school.urn, school.school_name)}`,
       lastModified: new Date(),
       changeFrequency: 'monthly',
       priority: 0.6,