docs: add build overview

packages/docs/build/index.mdx

@@ -0,0 +1,24 @@
+---
+title: "Build"
+description: "Build on the engine used by millions daily."
+mode: "wide"
+---
+
+<CardGroup cols={1}>
+  <Card title="Extend OpenCode" href="/build/plugins">
+    Build plugins that add tools, integrations, commands, agents, and custom behavior while keeping the rest of OpenCode
+    intact.
+  </Card>
+  <Card title="Run it as a server" href="/build/client">
+    Connect to OpenCode with the same client used by the TUI and desktop app, then build any interface, workflow, or agent
+    experience around it.
+  </Card>
+  <Card title="Embed it" href="/build/sdk">
+    Embed OpenCode directly into your application and build a completely custom agent, interface, or developer product
+    around it.
+  </Card>
+</CardGroup>
+
+<Warning>
+  The plugin API, client, and SDK are still being finalized during beta and may change before OpenCode 2.0 is stable.
+</Warning>

packages/docs/docs.json

@@ -46,12 +46,7 @@
       },
       {
         "tab": "Build",
-        "groups": [
-          {
-            "group": "Build with OpenCode",
-            "pages": ["build/plugins", "build/client", "build/sdk"]
-          }
-        ]
+        "pages": ["build/index", "build/plugins", "build/client", "build/sdk"]
       },
       {
         "tab": "API",