feat: Add metadata and descriptions to various documentation pages in Chinese

- Added titles and descriptions to workspace usage, configuration, customization, design principles, installation, integration guide, lead agent, MCP integration, memory system, middleware, quick start, sandbox, skills, subagents, and tools documentation.
- Removed outdated API/Gateway reference and concepts glossary pages.
- Updated configuration reference to reflect current structure and removed unnecessary sections.
- Introduced new model provider documentation for Ark and updated the index page for model providers.
- Enhanced tutorials with titles and descriptions for better clarity and navigation.

frontend/src/content/en/tutorials/create-your-first-harness.mdx

@@ -1,3 +1,8 @@
+---
+title: Create Your First Harness
+description: This tutorial shows you how to use the DeerFlow Harness programmatically — importing and using DeerFlow directly in your Python code rather than through the web interface.
+---
+
 import { Callout, Steps } from "nextra/components";
 
 # Create Your First Harness

frontend/src/content/en/tutorials/deploy-your-own-deerflow.mdx

@@ -1,3 +1,8 @@
+---
+title: Deploy Your Own DeerFlow
+description: This tutorial guides you through deploying DeerFlow to a production environment using Docker Compose for multi-user access.
+---
+
 import { Callout, Steps } from "nextra/components";
 
 # Deploy Your Own DeerFlow

frontend/src/content/en/tutorials/first-conversation.mdx

@@ -1,3 +1,8 @@
+---
+title: First Conversation
+description: This tutorial walks you through your first complete agent conversation in DeerFlow — from launching the app to getting meaningful work done with the agent.
+---
+
 import { Callout, Steps } from "nextra/components";
 
 # First Conversation

frontend/src/content/en/tutorials/use-tools-and-skills.mdx

@@ -1,3 +1,8 @@
+---
+title: Use Tools and Skills
+description: This tutorial shows you how to configure and use tools and skills in DeerFlow to give the agent access to web search, file operations, and domain-specific capabilities.
+---
+
 import { Callout } from "nextra/components";
 
 # Use Tools and Skills

frontend/src/content/en/tutorials/work-with-memory.mdx

@@ -1,3 +1,8 @@
+---
+title: Work with Memory
+description: This tutorial shows you how to enable and use DeerFlow's memory system so the agent remembers important information about you across multiple sessions.
+---
+
 import { Callout } from "nextra/components";
 
 # Work with Memory