fix(editor): render strikethrough on links (#15109)

**Issue**

Strikethrough on a link doesn't render. The toolbar button highlights
but no line
appears (#15106).

**Solution**

affine-link hardcoded text-decoration: none in the override it passes to
affineTextStyles, which clobbered the decoration computed from
strike/underline.
Removing it fixes the render; plain links still show no underline
because
affineTextStyles returns none by default.

**Result**

Strikethrough and underline render on links again. Added an e2e test: a
plain link
stays undecorated, a struck link renders line-through, red before the
fix and green
after.

fix #15106

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Bug Fixes**
* Fixed link text-decoration styling to properly support strikethrough
and other text formatting when applied to links.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/inlines/link/src/link-node/affine-link.ts

@@ -160,7 +160,6 @@ export class AffineLink extends WithDisposable(ShadowlessElement) {
     const linkStyle = {
       color: 'var(--affine-link-color)',
       fill: 'var(--affine-link-color)',
-      'text-decoration': 'none',
       cursor: 'pointer',
     };
 

tests/blocksuite/e2e/link.spec.ts

@@ -16,6 +16,7 @@ import {
   selectAllByKeyboard,
   setSelection,
   SHORT_KEY,
+  strikethrough,
   switchReadonly,
   type,
   waitNextFrame,
@@ -421,3 +422,35 @@ test('convert link to embed', async ({ page }, testInfo) => {
   await waitNextFrame(page);
   await expect(toolbar).toBeVisible();
 });
+
+test('strikethrough applies to a link', async ({ page }) => {
+  const linkText = 'linkText';
+  const link = 'http://example.com';
+  await enterPlaygroundRoom(page);
+  await initEmptyParagraphState(page);
+  await focusRichText(page);
+  await type(page, linkText);
+
+  // turn the selected text into a link
+  await dragBetweenIndices(page, [0, 0], [0, 8]);
+  await pressCreateLinkShortCut(page);
+  await page.mouse.move(0, 0);
+  const linkPopoverInput = page.locator('.affine-link-popover-input');
+  await expect(linkPopoverInput).toBeVisible();
+  await type(page, link);
+  await pressEnter(page);
+
+  const linkLocator = page.locator('affine-link a');
+  await expect(linkLocator).toHaveAttribute('href', link);
+
+  // a plain link keeps no text-decoration (preserve the default of no underline)
+  await expect(linkLocator).toHaveCSS('text-decoration-line', 'none');
+
+  // re-select the link text and strike it through
+  await dragBetweenIndices(page, [0, 0], [0, 8]);
+  await strikethrough(page);
+  await page.mouse.move(0, 0);
+
+  // regression for #15106: the strike must actually render on the link
+  await expect(linkLocator).toHaveCSS('text-decoration-line', 'line-through');
+});