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/slider.test.ts

@@ -0,0 +1,46 @@
+import {
+    expect,
+    test,
+} from './fixtures';
+
+/**
+ * Slider position is spring-animated; aria-valuenow reflects the current
+ * value, not the target. All assertions use `toHaveAttribute` so Playwright
+ * polls until the spring settles.
+ */
+test.describe('comparison slider', () => {
+    test.beforeEach(async ({ comparison }) => {
+        await comparison.pickPair('Inter', 'Roboto');
+        await comparison.slider.focus();
+    });
+
+    test('keyboard navigation snaps to End and Home', async ({ comparison }) => {
+        await comparison.slider.press('End');
+        await expect(comparison.slider).toHaveAttribute('aria-valuenow', '100');
+
+        await comparison.slider.press('Home');
+        await expect(comparison.slider).toHaveAttribute('aria-valuenow', '0');
+    });
+
+    test('arrow keys nudge by one, Shift+Arrow by ten', async ({ comparison }) => {
+        await comparison.slider.press('Home');
+        await expect(comparison.slider).toHaveAttribute('aria-valuenow', '0');
+
+        await comparison.slider.press('ArrowRight');
+        await expect(comparison.slider).toHaveAttribute('aria-valuenow', '1');
+
+        await comparison.slider.press('Shift+ArrowRight');
+        await expect(comparison.slider).toHaveAttribute('aria-valuenow', '11');
+    });
+
+    test('PageUp / PageDown move by ten', async ({ comparison }) => {
+        await comparison.slider.press('Home');
+        await expect(comparison.slider).toHaveAttribute('aria-valuenow', '0');
+
+        await comparison.slider.press('PageUp');
+        await expect(comparison.slider).toHaveAttribute('aria-valuenow', '10');
+
+        await comparison.slider.press('PageDown');
+        await expect(comparison.slider).toHaveAttribute('aria-valuenow', '0');
+    });
+});