init: seed framework reference content from agent-runtimes main repo

harnesses/composites/spec-writing-opus-repo/v1/harness.yaml

@@ -0,0 +1,10 @@
+kind: composite
+name: spec-writing-opus-repo
+version: 1
+description: "Spec writing agent with Opus + repo clone via SSH"
+
+layers:
+  - context: spec-writing/v1
+  - context: anthropic-cloud/v1
+  - context: gitea-ssh/v1
+  - context: agent-repo/v1