feat(core): support compose a doc tool (#13013)

#### PR Dependency Tree


* **PR #13013** 👈

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

* **New Features**
* Introduced a document composition tool for AI chat, allowing users to
generate, preview, and save structured markdown documents directly from
chat interactions.
* Added an artifact preview panel for enhanced document previews within
the chat interface.
* Enabled dynamic content rendering in the chat panel's right section
for richer user experiences.

* **Improvements**
  * Sidebar maximum width increased for greater workspace flexibility.
* Enhanced chat message and split view styling for improved layout and
usability.

* **Bug Fixes**
  * None.

* **Other**
* Registered new custom elements for AI tools and artifact preview
functionality.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/tools/doc-compose.ts

@@ -0,0 +1,70 @@
+import { Logger } from '@nestjs/common';
+import { tool } from 'ai';
+import { z } from 'zod';
+
+import { toolError } from './error';
+
+const logger = new Logger('DocComposeTool');
+
+export const createDocComposeTool = () => {
+  return tool({
+    description:
+      'Write a new document with markdown content. This tool creates structured markdown content for documents including titles, sections, and formatting.',
+    parameters: z.object({
+      title: z.string().describe('The title of the document'),
+      content: z
+        .string()
+        .describe(
+          'The main content to write in markdown format. Include proper markdown formatting like headers (# ## ###), lists (- * 1.), links [text](url), code blocks ```code```, and other markdown elements as needed.'
+        ),
+      sections: z
+        .array(
+          z.object({
+            heading: z.string().describe('Section heading'),
+            content: z.string().describe('Section content in markdown'),
+          })
+        )
+        .optional()
+        .describe('Optional structured sections for the document'),
+      metadata: z
+        .object({
+          tags: z
+            .array(z.string())
+            .optional()
+            .describe('Optional tags for the document'),
+          description: z
+            .string()
+            .optional()
+            .describe('Optional brief description of the document'),
+        })
+        .optional()
+        .describe('Optional metadata for the document'),
+    }),
+    execute: async ({ title, content, sections, metadata }) => {
+      try {
+        let markdownContent = '';
+
+        markdownContent += `${content}\n\n`;
+
+        if (sections && sections.length > 0) {
+          for (const section of sections) {
+            markdownContent += `## ${section.heading}\n\n`;
+            markdownContent += `${section.content}\n\n`;
+          }
+        }
+
+        return {
+          title,
+          markdown: markdownContent.trim(),
+          wordCount: content.split(/\s+/).length,
+          metadata: metadata || {},
+          tags: metadata?.tags || [],
+          description: metadata?.description || '',
+        };
+      } catch (err: any) {
+        logger.error(`Failed to write document: ${title}`, err);
+        return toolError('Doc Write Failed', err.message);
+      }
+    },
+  });
+};