test: add e2e suite for core comparison flows

Adds 17 new specs across six files plus the supporting POM
infrastructure:

- fixtures with auto-opened comparison + typography helpers
- TypographyMenu POM reading values from ComboControl aria-labels
- ComparisonPage extended with side selection, font picking,
  slider-value reader, FontFaceSet inspection, storage snapshot
- compare-flow: A/B selection, aria-pressed state, storage write
- preview-text: input binding + slider character rendering
- slider: keyboard ARIA contract (Arrow / Shift+Arrow / Page / Home / End)
- font-loading: FontFaceSet contains selected, excludes unrelated
- persistence: font selection + typography settings survive reload
- typography: symmetric increase/decrease for all four controls

e2e/fixtures.ts

@@ -0,0 +1,35 @@
+import { test as base } from '@playwright/test';
+import { ComparisonPage } from './pages/comparison-page';
+import { TypographyMenu } from './pages/typography-menu';
+
+type Fixtures = {
+    /**
+     * Opened ComparisonPage with the root view loaded.
+     */
+    comparison: ComparisonPage;
+    /**
+     * Typography menu helper bound to the same page.
+     */
+    typography: TypographyMenu;
+};
+
+/**
+ * Custom test that auto-opens the comparison view before each spec.
+ * Playwright gives each test a fresh BrowserContext by default, so
+ * localStorage is empty unless a test seeds it.
+ */
+export const test = base.extend<Fixtures>({
+    comparison: async ({ page }, use) => {
+        const view = new ComparisonPage(page);
+        await view.open();
+        await use(view);
+    },
+    // Depends on `comparison` so the root page is opened before the menu is
+    // consulted — TypographyMenu has no markup of its own to load.
+    typography: async ({ comparison, page }, use) => {
+        void comparison;
+        await use(new TypographyMenu(page));
+    },
+});
+
+export { expect } from '@playwright/test';