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- Removed outdated API/Gateway reference and concepts glossary pages.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/reference/_meta.ts

@@ -1,20 +1,8 @@
 import type { MetaRecord } from "nextra";
 
 const meta: MetaRecord = {
-  "concepts-glossary": {
-    title: "Concepts Glossary",
-  },
-  "configuration-reference": {
-    title: "Configuration Reference",
-  },
-  "api-gateway-reference": {
-    title: "API / Gateway Reference",
-  },
-  "runtime-flags-and-modes": {
-    title: "Runtime Flags and Modes",
-  },
-  "source-map": {
-    title: "Source Map",
+  "model-providers": {
+    title: "Model providers",
   },
 };