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/ComparisonView.tsx

@@ -13,7 +13,7 @@ import { SchoolSearchModal } from './SchoolSearchModal';
 import { EmptyState } from './EmptyState';
 import { LoadingSkeleton } from './LoadingSkeleton';
 import type { ComparisonData, MetricDefinition, School } from '@/lib/types';
-import { formatPercentage, formatProgress, CHART_COLORS } from '@/lib/utils';
+import { formatPercentage, formatProgress, CHART_COLORS, schoolUrl } from '@/lib/utils';
 import { fetchComparison } from '@/lib/api';
 import styles from './ComparisonView.module.css';
 
@@ -305,7 +305,7 @@ export function ComparisonView({
                     ×
                   </button>
                   <h2 className={styles.schoolName}>
-                    <a href={`/school/${school.urn}`}>{school.school_name}</a>
+                    <a href={schoolUrl(school.urn, school.school_name)}>{school.school_name}</a>
                   </h2>
                   <div className={styles.schoolMeta}>
                     {school.local_authority && (