feat: database layer + canvas validator/converter + LLM inference activities

- Add pkg/db models and CRUD methods for workflows
- Add internal/routing canvas validator (DAG check, connectivity)
- Add internal/routing canvas converter (Canvas → WorkflowSpec)
- Register LLMInferenceActivity and LLMBatchInferenceActivity
- Update api/server and cmd/server with database integration
- Add K8s environment variable support
- Update activity knowledge base with LLM activities
- Add .env.example configuration template

k8s/git-commit.yaml

@@ -9,6 +9,6 @@ metadata:
     app.kubernetes.io/name: poimen
     app.kubernetes.io/component: orchestrator
 data:
-  GIT_COMMIT: "cdb6efe2"  # Updated automatically by CI/CD
+  GIT_COMMIT: "e07b9504"  # Updated automatically by CI/CD
   GIT_BRANCH: "main"
-  DEPLOYMENT_DATE: "2026-09-04"
+  DEPLOYMENT_DATE: "2026-09-05"