refactor(core): add keyPress event to fix IME space detection (#11700)

### TL;DR
Refactor space-triggered AI Widget activation logic from `keydown` to `keypress` event listeners

### Background

The `keydown` event triggered by a space may originate from:
1. Normal space insertion
2. Space triggered by input method confirming candidate words

In scenarios like (2), some browsers (see [ISSUE](https://github.com/toeverything/AFFiNE/issues/11541)) and input method callbacks produce events identical to scenario (1),making it impossible to distinguish between the two.

To fix this, the space-activated AI listener uses the `keypress` event:
In scenario 2, `event.which !== 32` (may be `30430` or other values) can be used to differentiate from scenario 1.

> CLOSE BS-3081

tests/affine-cloud-copilot/e2e/basic/guidance.spec.ts

@@ -0,0 +1,18 @@
+import { expect } from '@playwright/test';
+
+import { test } from '../base/base-test';
+
+test.describe('AIBasic/Guidance', () => {
+  test.beforeEach(async ({ page, utils }) => {
+    await utils.testUtils.setupTestEnvironment(page);
+  });
+
+  test('should show AI panel when space is pressed on empty paragraph', async ({
+    page,
+    utils,
+  }) => {
+    await utils.editor.focusToEditor(page);
+    await page.keyboard.press('Space');
+    await expect(page.locator('affine-ai-panel-widget')).toBeVisible();
+  });
+});