feat(core): add section edit tool (#13313)

Close [AI-396](https://linear.app/affine-design/issue/AI-396)

<img width="798" height="294" alt="截屏2025-07-25 11 30 32"
src="https://github.com/user-attachments/assets/6366dab2-688b-470b-8b24-29a2d50a38c9"
/>



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

## Summary by CodeRabbit

* **New Features**
* Introduced a "Section Edit" AI tool for expert editing of specific
markdown sections based on user instructions, preserving formatting and
style.
* Added a new interface and UI component for section editing, allowing
users to view, copy, insert, or save edited content directly from chat
interactions.

* **Improvements**
* Enhanced AI chat and tool rendering to support and display section
editing results.
* Updated chat input handling for improved draft management and message
sending order.

* **Other Changes**
* Registered the new section editing tool in the system for seamless
integration.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/prompt/prompts.ts

@@ -1468,6 +1468,29 @@ When sent new notes, respond ONLY with the contents of the html file.`,
       },
     ],
   },
+  {
+    name: 'Section Edit',
+    action: 'Section Edit',
+    model: 'claude-sonnet-4@20250514',
+    messages: [
+      {
+        role: 'system',
+        content: `You are an expert text editor. Your task is to modify the provided text content according to the user's specific instructions while preserving the original formatting and style. 
+Key requirements:
+- Follow the user's instructions precisely
+- Maintain the original markdown formatting
+- Preserve the tone and style unless specifically asked to change it
+- Only make the requested changes
+- Return only the modified text without any explanations or comments`,
+      },
+      {
+        role: 'user',
+        content: `Please modify the following text according to these instructions: "{{instructions}}"
+Original text:
+{{content}}`,
+      },
+    ],
+  },
 ];
 
 const imageActions: Prompt[] = [
@@ -1924,7 +1947,7 @@ Below is the user's query. Please respond in the user's preferred language witho
   config: {
     tools: [
       'docRead',
-      'docEdit',
+      'sectionEdit',
       'docKeywordSearch',
       'docSemanticSearch',
       'webSearch',