refactor(agent): extract agent+shared into standalone packages with full GRACE semantic markup

- Move agent code from backend/src/agent/ to agent/src/ss_tools/agent/
- Extract shared stdlib-only utilities to shared/src/ss_tools/shared/
- Add #region/#endregion contracts to all ~140 functions (INV_1 compliance)
- Update docker files, entrypoint, build scripts for new package layout
- Backend now imports ss_tools.shared._llm_health (no gradio/langchain deps)
- Add specs for 036-039 feature plans

backend/src/api/routes/__init__.py

@@ -22,6 +22,7 @@ __all__ = [
     "admin",
     "admin_api_keys",
     "agent_conversations",
+    "agent_status",
     "agent_superset",
     "agent_superset_explore",
     "assistant",