feat(leaderboard): enhance preferred language leaderboard loading

Trigger preferred language leaderboard refresh on component 
initialization instead of instance initializer to ensure the service 
boots after authenticator is available. Update header tests to 
verify leaderboard link changes dynamically based on user's 
leaderboard entries and feature flag. This improves leaderboard 
loading accuracy and user navigation consistency.

Author: rohitpaulk

app/components/header/index.ts

@@ -32,6 +32,13 @@ export default class Header extends Component<Signature> {
   @tracked floatingBarStyle: SafeString = htmlSafe('left: 0px; width: 0px; opacity: 0;');
   @tracked floatingBarContainer: HTMLElement | null = null;
 
+  constructor(owner: unknown, args: object) {
+    super(owner, args);
+
+    // This can't be in instance-initializers since it depends on the authenticator service
+    this.preferredLanguageLeaderboard.onBoot();
+  }
+
   get activeDiscountForYearlyPlan(): PromotionalDiscountModel | null {
     return this.currentUser?.activeDiscountForYearlyPlan || null;
   }

app/instance-initializers/preferred-language-leaderboard.ts

@@ -53,10 +53,12 @@ export default class PreferredLanguageLeaderboardService extends Service {
     const serializedStoredData = this.localStorage.getItem(PreferredLanguageLeaderboardService.STORAGE_KEY);
 
     if (!serializedStoredData) {
+      await this.refresh();
+
       return;
     }
 
-    // Let's use the latest value we have from
+    // Let's use the latest value we have from local storage
     const storedData = StoredData.fromJSON(serializedStoredData);
     this.preferredLanguageSlugs = storedData.languageSlugs;
 

app/services/preferred-language-leaderboard.ts

@@ -30,15 +30,34 @@ module('Acceptance | header-test', function (hooks) {
     assert.strictEqual(currentURL(), '/pay', 'expect to be redirected to pay page');
   });
 
-  test('header should show leaderboard link if user is authenticated and has feature flag enabled', async function (assert) {
+  test('header should show generic leaderboard link if user has feature flag enabled and leaderboard entries', async function (assert) {
     const user = signIn(this.owner, this.server);
     user.update('featureFlags', { 'should-see-leaderboard': 'true' });
 
     await catalogPage.visit();
     assert.true(catalogPage.header.hasLink('Leaderboard'), 'expect leaderboard link to be visible');
 
     await catalogPage.header.clickOnHeaderLink('Leaderboard');
-    assert.strictEqual(currentURL(), '/leaderboards/rust', 'expect to be redirected to rust leaderboard page by default');
+    assert.strictEqual(currentURL(), '/leaderboards/rust', 'expect to be redirected to rust leaderboard page');
+  });
+
+  test('header should show custom leaderboard link if user has feature flag enabled', async function (assert) {
+    const user = signIn(this.owner, this.server);
+    user.update('featureFlags', { 'should-see-leaderboard': 'true' });
+
+    const python = this.server.schema.languages.findBy({ name: 'Python' });
+
+    this.server.create('leaderboard-entry', {
+      leaderboard: python.leaderboard,
+      user: user,
+      score: 100,
+    });
+
+    await catalogPage.visit();
+    assert.true(catalogPage.header.hasLink('Leaderboard'), 'expect leaderboard link to be visible');
+
+    await catalogPage.header.clickOnHeaderLink('Leaderboard');
+    assert.strictEqual(currentURL(), '/leaderboards/python', 'expect to be redirected to python leaderboard page');
   });
 
   test('header should show upgrade button if user does not have an active subscription', async function (assert) {