feat(registry): añade FileSystemPolicyStore con carga YAML versionada

Incluye 'yaml' en los overrides de mypy (PyYAML no trae type stubs).

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

core/src/agentforge_core/registry/policy_store.py

@@ -0,0 +1,64 @@
+"""PolicyStore basado en sistema de ficheros (YAML por versión + index.yaml)."""
+
+from __future__ import annotations
+
+from datetime import datetime
+from pathlib import Path
+from typing import Any
+
+import yaml
+
+from agentforge_core.domain.policy import PolicyDefinition, PolicyVersionMeta
+
+
+class FileSystemPolicyStore:
+    """Lee políticas de policies/<name>/{index.yaml,versions/vN.yaml}."""
+
+    def __init__(self, root: Path) -> None:
+        self._root = Path(root)
+
+    def list_policies(self) -> list[PolicyDefinition]:
+        if not self._root.exists():
+            return []
+        result: list[PolicyDefinition] = []
+        for d in sorted(self._root.iterdir()):
+            if d.is_dir() and (d / "index.yaml").exists():
+                result.append(self.get_policy(d.name))
+        return result
+
+    def get_policy(self, name: str, version: str | None = None) -> PolicyDefinition:
+        index = self._load_index(name)
+        v = version or index["active_version"]
+        path = self._root / name / "versions" / f"{v}.yaml"
+        if not path.exists():
+            raise FileNotFoundError(f"policy version not found: {name}@{v}")
+        with path.open(encoding="utf-8") as f:
+            data = yaml.safe_load(f)
+        return PolicyDefinition.model_validate(data)
+
+    def list_versions(self, name: str) -> list[PolicyVersionMeta]:
+        index = self._load_index(name)
+        return [
+            PolicyVersionMeta(
+                id=v["id"],
+                hash=v["hash"],
+                author=v["author"],
+                message=v["message"],
+                created_at=self._parse_dt(v["created_at"]),
+            )
+            for v in index["versions"]
+        ]
+
+    def _load_index(self, name: str) -> dict[str, Any]:
+        index_path = self._root / name / "index.yaml"
+        if not index_path.exists():
+            raise FileNotFoundError(f"policy not found: {name}")
+        with index_path.open(encoding="utf-8") as f:
+            data: dict[str, Any] = yaml.safe_load(f)
+        return data
+
+    @staticmethod
+    def _parse_dt(value: str | datetime) -> datetime:
+        if isinstance(value, datetime):
+            return value
+        return datetime.fromisoformat(value.replace("Z", "+00:00"))