feat(flywheel): 新增 GoldenCase 模型用于规则回归门禁

- 新增 golden_cases 表，承载版本化的风险规则黄金用例
  （case_key/rule_code/values_json/expected_hit/expected_severity/status）
- 注册到 db/base.py 和 models/__init__.py，进入 Base.metadata

server/src/app/models/golden_case.py

@@ -0,0 +1,48 @@
+from __future__ import annotations
+
+import uuid
+from datetime import datetime
+from typing import Any
+
+from sqlalchemy import Boolean, DateTime, Index, String, Text, func
+from sqlalchemy.orm import Mapped, mapped_column
+from sqlalchemy.types import JSON
+
+from app.db.base_class import Base
+
+
+class GoldenCase(Base):
+    """风险规则回归门禁用的黄金用例。
+
+    由运营手动维护（或从已确认风险观测导入），在规则发布前作为回归集执行，
+    100% 通过才放行。``values_json`` 复用 ``AgentAssetRiskRuleSampleCase.values``
+    的扁平字典格式，``expected_hit`` / ``expected_severity`` 作为 ground truth。
+    """
+
+    __tablename__ = "golden_cases"
+    __table_args__ = (
+        Index("ix_golden_cases_rule_code_status", "rule_code", "status"),
+        Index("ix_golden_cases_scene_status", "scene", "status"),
+    )
+
+    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
+    case_key: Mapped[str] = mapped_column(String(160), unique=True, index=True)
+    rule_code: Mapped[str | None] = mapped_column(String(120), nullable=True, index=True)
+    scene: Mapped[str] = mapped_column(String(50), default="", index=True)
+
+    name: Mapped[str] = mapped_column(String(120), default="")
+    values_json: Mapped[dict[str, Any]] = mapped_column(JSON, default=dict)
+    expected_hit: Mapped[bool] = mapped_column(Boolean, default=True)
+    expected_severity: Mapped[str | None] = mapped_column(String(20), nullable=True)
+    note: Mapped[str | None] = mapped_column(Text(), nullable=True)
+
+    status: Mapped[str] = mapped_column(String(20), default="active", index=True)
+    source: Mapped[str] = mapped_column(String(30), default="manual")
+
+    created_at: Mapped[datetime] = mapped_column(DateTime, default=func.now(), server_default=func.now())
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime,
+        default=func.now(),
+        onupdate=func.now(),
+        server_default=func.now(),
+    )