initial: test-helper agent for e2e platform feature coverage

Two skills:
  - echo(text): trivial sub-second response. Used by approval-mode tests
    that need a fast handoff target.
  - try_scope_expansion(reason, read_patterns, ttl_seconds, mode):
    deliberately calls ctx.request_scope() with caller-supplied args so
    e2e tests can exercise the orchestrator's scope-negotiation flow
    end-to-end without inventing a real workload that happens to need
    extra files.

Standard A2A scaffold: Dockerfile FROM a2a-pack-base, /invoke/{skill} +
/.well-known/agent-card served by the SDK's serve/asgi.py adapter, deploy/
manifests for k8s, Gitea Actions workflow that builds + bumps the image
SHA.

Public, low resources (50m CPU / 128Mi mem). Not exposed via the public
ingress in any meaningful way — only the in-cluster Service is consulted
by the orchestrator's call_agent.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

requirements.txt

@@ -0,0 +1 @@
+pydantic>=2.6