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/lib/utils.ts

@@ -20,6 +20,28 @@ export function slugify(text: string): string {
     .trim();
 }
 
+/**
+ * Build a school URL path: /school/123456-school-name (capped at ~80 chars total)
+ */
+const MAX_SLUG_LENGTH = 60;
+
+export function schoolUrl(urn: number, schoolName?: string): string {
+  if (!schoolName) return `/school/${urn}`;
+  let slug = slugify(schoolName);
+  if (slug.length > MAX_SLUG_LENGTH) {
+    slug = slug.slice(0, MAX_SLUG_LENGTH).replace(/-+$/, '');
+  }
+  return `/school/${urn}-${slug}`;
+}
+
+/**
+ * Extract the URN from a school slug (e.g. "138267-some-school-name" → 138267)
+ */
+export function parseSchoolSlug(slug: string): number | null {
+  const match = slug.match(/^(\d{6})/);
+  return match ? parseInt(match[1], 10) : null;
+}
+
 /**
  * Escape HTML to prevent XSS
  */