Add championship what-if simulator

Fourth view on the championship page: assign P1-P10 per remaining
round and see projected standings update live, with position deltas
and mathematically alive/eliminated title states. Pure projection
logic in lib/simulator.ts (2025 points system, standard GPs only);
scenarios persist to localStorage per season. 169 frontend tests
passing.

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

frontend/src/test/setup.ts

@@ -4,3 +4,26 @@ Object.defineProperty(window, 'scrollTo', {
   value: () => {},
   writable: true,
 })
+
+// Node 22+ ships an experimental `localStorage` global that shadows jsdom's
+// implementation; without `--localstorage-file` it resolves to undefined in
+// the test environment. Back-fill a minimal in-memory Storage so components
+// that persist state (e.g. the championship simulator) are testable.
+if (typeof window !== 'undefined' && !window.localStorage) {
+  const store = new Map<string, string>()
+  const localStorageMock: Storage = {
+    get length() {
+      return store.size
+    },
+    clear: () => store.clear(),
+    getItem: (key) => (store.has(key) ? store.get(key)! : null),
+    key: (index) => [...store.keys()][index] ?? null,
+    removeItem: (key) => {
+      store.delete(key)
+    },
+    setItem: (key, value) => {
+      store.set(String(key), String(value))
+    },
+  }
+  Object.defineProperty(window, 'localStorage', { value: localStorageMock, writable: true })
+}