refactor(api): Phase 16 R2 封存死代碼 + RiskLevel 統一

封存 (866 行):
- routes/approvals.py → _archived/routes/ (477 行，未註冊死代碼)
- services/approval.py → _archived/services/ (389 行，僅被死代碼使用)

合併 RiskLevel:
- models/approval.py 新增 HIGH (從 trust_engine.py 合併)
- trust_engine.py 改 import from models/approval.py
- 保留舊定義為註解供回滾

更新 services/__init__.py:
- 移除已封存模組的 import (註解保留回滾路徑)

驗證:
- RiskLevel 統一: models 與 trust_engine 使用同一 class
- 24 個 action_parsing 測試通過

回滾指令見 _archived/README.md

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/src/services/__init__.py

@@ -1,23 +1,28 @@
 """
 AWOOOI API Services
+
+變更紀錄:
+- 2026-03-25 Phase 16 R2: 移除 .approval import (已封存至 _archived/)
 """
 
-from .approval import (
-    RISK_MATRIX,
-    ApprovalAlreadyDecidedError,
-    # Exceptions
-    ApprovalError,
-    ApprovalNotFoundError,
-    ApprovalState,
-    ApprovalStatus,
-    DuplicateSignatureError,
-    InsufficientPermissionError,
-    MultiSigEngine,
-    Signature,
-    TOCTOUConflictError,
-    UserRole,
-    multi_sig_engine,
-)
+# Phase 16 R2 (2026-03-25): 以下 import 已封存，原模組移至 _archived/services/approval.py
+# 回滾: 將 _archived/services/approval.py 移回，取消下方註解
+# from .approval import (
+#     RISK_MATRIX,
+#     ApprovalAlreadyDecidedError,
+#     ApprovalError,
+#     ApprovalNotFoundError,
+#     ApprovalState,
+#     ApprovalStatus,
+#     DuplicateSignatureError,
+#     InsufficientPermissionError,
+#     MultiSigEngine,
+#     Signature,
+#     TOCTOUConflictError,
+#     UserRole,
+#     multi_sig_engine,
+# )
+
 from .consensus_engine import (
     AgentOpinion,
     AgentType,
@@ -54,21 +59,20 @@ __all__ = [
     "DryRunEngine",
     "DryRunResult",
     "dry_run_engine",
-    # Multi-Sig
-    "MultiSigEngine",
-    "multi_sig_engine",
-    "ApprovalState",
-    "Signature",
-    "UserRole",
-    "ApprovalStatus",
-    "RISK_MATRIX",
-    # Exceptions
-    "ApprovalError",
-    "InsufficientPermissionError",
-    "DuplicateSignatureError",
-    "TOCTOUConflictError",
-    "ApprovalNotFoundError",
-    "ApprovalAlreadyDecidedError",
+    # Phase 16 R2: Multi-Sig 已封存至 _archived/services/approval.py
+    # "MultiSigEngine",
+    # "multi_sig_engine",
+    # "ApprovalState",
+    # "Signature",
+    # "UserRole",
+    # "ApprovalStatus",
+    # "RISK_MATRIX",
+    # "ApprovalError",
+    # "InsufficientPermissionError",
+    # "DuplicateSignatureError",
+    # "TOCTOUConflictError",
+    # "ApprovalNotFoundError",
+    # "ApprovalAlreadyDecidedError",
     # Trust Engine
     "TrustScoreManager",
     "trust_engine",