feat(core): add location-scoped config loading

packages/core/test/fixture/location.ts

@@ -0,0 +1,12 @@
+import { Location } from "@opencode-ai/core/location"
+import { Project } from "@opencode-ai/core/project"
+import { AbsolutePath } from "@opencode-ai/core/schema"
+
+export function location(ref: Location.Ref, input: { projectDirectory?: AbsolutePath; vcs?: Project.Vcs } = {}) {
+  return {
+    directory: ref.directory,
+    workspaceID: ref.workspaceID,
+    project: { id: Project.ID.global, directory: input.projectDirectory ?? ref.directory },
+    vcs: input.vcs,
+  } satisfies Location.Interface
+}