feat: cleanup chat panel (#14259)

#### PR Dependency Tree


* **PR #14258**
  * **PR #14259** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

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

* **Refactor**
* Split AI initialization into separate editor, app, and shared
registries; removed legacy chat-panel and replaced it with a
component-based editor chat, updating wiring and public exports.
* Propagated server/subscription/model services into chat/playground
components and improved session lifecycle and UI composition.

* **Tests**
* Added tests for AI effect registration and chat session resolution;
extended DOM/test utilities and assertions.

* **Chores**
  * Added happy-dom for runtime and test environments.

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tests/affine-local/e2e/ai-land.spec.ts

@@ -13,5 +13,5 @@ test('Click ai-land icon', async ({ page }) => {
   await clickNewPageButton(page);
   await page.locator('[data-testid=ai-island]').click();
 
-  await expect(page.locator('chat-panel')).toBeVisible();
+  await expect(page.getByTestId('chat-panel-input-container')).toBeVisible();
 });