feat(domain): añade modelos GuardrailViolation, PolicyDefinition y AgentExecution

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/unit/test_domain_policy.py

@@ -0,0 +1,14 @@
+"""Tests del modelo PolicyDefinition."""
+
+from agentforge_core.domain.policy import PolicyDefinition, PolicyValidator
+
+
+def test_policy_definition_default_fail_closed() -> None:
+    p = PolicyDefinition(
+        name="default",
+        version="v1",
+        description="x",
+        input_validators=[PolicyValidator(type="detect_pii", config={})],
+        output_validators=[],
+    )
+    assert p.on_validator_error == "fail_closed"