fix: register opencode image understanding

extensions/opencode/plugin-registration.contract.test.ts

@@ -0,0 +1,8 @@
+import { describePluginRegistrationContract } from "../../test/helpers/plugins/plugin-registration-contract.js";
+
+describePluginRegistrationContract({
+  pluginId: "opencode",
+  providerIds: ["opencode"],
+  mediaUnderstandingProviderIds: ["opencode"],
+  requireDescribeImages: true,
+});