feat(tui): discover project plugins

.opencode/plugins/tui/discovery-smoke.ts

@@ -0,0 +1,16 @@
+import type { Context } from "../../../packages/plugin/src/tui/context"
+
+export default {
+  id: "test.tui-discovery-smoke",
+  setup(context: Context) {
+    const timer = setTimeout(() => {
+      context.ui.toast.show({
+        title: "TUI plugin discovery works",
+        message: "Loaded .opencode/plugins/tui/discovery-smoke.ts",
+        variant: "success",
+        duration: 30_000,
+      })
+    }, 1_000)
+    return () => clearTimeout(timer)
+  },
+}