fix(gate-quality): trust_engine_v2 类型注解用 TYPE_CHECKING 导入

[frankiehot-tech]

摘要

gate-quality 的 ruff check src/maref src/maref_lite 在 CI 上仍失败，此前（PR #302）只修了 __init__.py 的 I001，但完整树检查发现 3 个 pre-existing 错误全部来自 src/maref/recursive/trust_engine_v2.py：

• F821 at 94:55 — def to_audit_record(...) -> UnifiedAuditRecord 注解中 UnifiedAuditRecord 未定义（lazy import 仅在函数体内）
• F821 at 148:37 — def __init__(self, audit_store: UnifiedAuditStore | None = None) 注解中 UnifiedAuditStore 未定义
• I001 at 1:1 — @dataclass 前缺双空行（import 块与顶层代码分隔）

修复

• from typing import TYPE_CHECKING, Any + if TYPE_CHECKING: 块引入两个类型（运行时惰性导入保留，无循环 import 风险）
• @dataclass 前补双空行

验证

• ruff check src/maref src/maref_lite → All checks passed!
• ruff format --check 目标文件 → already formatted
• 未新增 /Volumes/ 硬编码路径（No hardcoded paths 步骤不受影响）
• 运行时行为不变：TYPE_CHECKING 为 False 时不执行导入，原函数体内惰性导入保留

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