refactor(core): move models.dev into core (#27347)

packages/core/src/instance.ts

@@ -0,0 +1,10 @@
+import { Context } from "effect"
+
+export * as Instance from "./instance"
+
+export type Ref = {
+  readonly directory: string
+  readonly workspaceID?: string
+}
+
+export class Service extends Context.Service<Service, Ref>()("@opencode/Instance") {}