feat(core): remove chat-panel component's dependency on doc (#12975)

Close [AI-259](https://linear.app/affine-design/issue/AI-259)
Close [AI-243](https://linear.app/affine-design/issue/AI-243)

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

* **New Features**
* Introduced a unified AI chat content component to manage and display
chat interactions.
* Added new chat block message components for improved chat message
rendering.

* **Refactor**
* Simplified and unified session management across all AI chat
components, now passing full session objects instead of session IDs.
* Updated component and property names for clarity and consistency
(e.g., chat message and block message components).
* Consolidated chat history and actions retrieval for a more streamlined
chat experience.
* Removed redundant session ID getters and replaced them with direct
session object usage.
* Streamlined chat panel and composer components by removing internal
message and context state management.

* **Bug Fixes**
* Improved handling of chat session state and loading, reducing
redundant state properties.
* Enhanced event handling to prevent errors when chat parameters are
missing.

* **Tests**
* Removed outdated chat clearing test cases to align with new chat state
management.

* **Chores**
* Updated import paths and reorganized module exports for better
maintainability.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

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

@@ -343,25 +343,6 @@ test.describe('AIBasic/Chat', () => {
     ]);
   });
 
-  test('should support clearing chat', async ({
-    loggedInPage: page,
-    utils,
-  }) => {
-    await utils.chatPanel.openChatPanel(page);
-    await utils.chatPanel.makeChat(page, 'Hello. Answer in 50 words.');
-    await utils.chatPanel.waitForHistory(page, [
-      {
-        role: 'user',
-        content: 'Hello. Answer in 50 words.',
-      },
-      {
-        role: 'assistant',
-        status: 'success',
-      },
-    ]);
-    await utils.chatPanel.clearChat(page);
-    await utils.chatPanel.waitForHistory(page, []);
-  });
   test('should support copying answer', async ({
     loggedInPage: page,
     utils,