test: add jsdom globals and school detail fixtures

jsdom provides neither IntersectionObserver nor scrollTo; both detail views
use them. Adds four fixtures (primary, secondary, all-through, special)
covering the branches the characterization tests will pin.

SchoolResult carries 57 required nullable fields, so fixtures are built from
an all-null base row and override only what they exercise.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

nextjs-app/jest.setup.js

@@ -27,6 +27,23 @@ Object.defineProperty(window, 'matchMedia', {
   })),
 });
 
+// jsdom implements neither of these; the school detail views use both
+// (IntersectionObserver for the scroll-spy and the hero-CTA tracker,
+// scrollTo for the "back to top" control).
+global.IntersectionObserver = class {
+  constructor(callback) {
+    this.callback = callback;
+  }
+  observe() {}
+  unobserve() {}
+  disconnect() {}
+  takeRecords() {
+    return [];
+  }
+};
+
+window.scrollTo = jest.fn();
+
 // Mock localStorage
 const localStorageMock = {
   getItem: jest.fn(),