(docs): Add ecosystem support section to MCP intro page (modelcontextprotocol#2359)

* Add broad ecosystem support section to intro page

Highlight the wide range of clients supporting MCP, including
Claude, ChatGPT, VS Code, Cursor, and MCPJam.

:house: Remote-Dev: homespace

* Add Build MCP apps card to intro page

:house: Remote-Dev: homespace

* Capitalize Apps in Build MCP Apps card

:house: Remote-Dev: homespace

* Fix Prettier formatting in intro.mdx

:house: Remote-Dev: homespace

Author: localden

docs/docs/getting-started/intro.mdx

@@ -28,15 +28,23 @@ Depending on where you sit in the ecosystem, MCP can have a range of benefits.
 - **AI applications or agents**: MCP provides access to an ecosystem of data sources, tools and apps which will enhance capabilities and improve the end-user experience.
 - **End-users**: MCP results in more capable AI applications or agents which can access your data and take actions on your behalf when necessary.
 
+## Broad ecosystem support
+
+MCP is an open protocol supported across a wide range of clients and servers. AI assistants like [Claude](https://claude.com/docs/connectors/building) and [ChatGPT](https://developers.openai.com/api/docs/mcp/), development tools like [Visual Studio Code](https://code.visualstudio.com/docs/copilot/chat/mcp-servers), [Cursor](https://cursor.com/docs/context/mcp), [MCPJam](https://docs.mcpjam.com/getting-started), and [many others](/clients) all support MCP — making it easy to build once and integrate everywhere.
+
 ## Start Building
 
 <CardGroup cols={2}>
   <Card title="Build servers" icon="server" href="/docs/develop/build-server">
     Create MCP servers to expose your data and tools
   </Card>
 
-  <Card title="Build clients" icon="computer" href="/docs/develop/build-client">
-    Develop applications that connect to MCP servers
+<Card title="Build clients" icon="computer" href="/docs/develop/build-client">
+  Develop applications that connect to MCP servers
+</Card>
+
+  <Card title="Build MCP Apps" icon="puzzle-piece" href="/extensions/apps/overview">
+    Build interactive apps that run inside AI clients
   </Card>
 </CardGroup>