Studio: add Unsloth Docs to the MCP server presets (#6633)

Adds Unsloth's GitBook docs MCP endpoint as a keyless preset in the
composer MCP menu, alongside Context7, Exa and Hugging Face.

studio/frontend/src/features/chat/mcp-composer-button.tsx

@@ -60,6 +60,11 @@ type McpPreset = {
 // Keyless remote MCP presets (rate-limited free tiers, no API key).
 // Hugging Face runs anonymously; add a token via "Manage MCP servers".
 const MCP_PRESETS: readonly McpPreset[] = [
+  {
+    id: "unsloth-docs",
+    displayName: "Unsloth Docs",
+    url: "https://unsloth.ai/docs/~gitbook/mcp",
+  },
   {
     id: "context7",
     displayName: "Context7",