fix(model): IncidentOutcome 舊 Redis 字串格式相容性

舊事件 outcome 存為字串 "resolved"，Pydantic v2 無法解析
→ INTERNAL_ERROR on /auto-repair/evaluate/{incident_id}

field_validator mode='before' 將字串轉為 None (安全丟棄)
確保舊資料不引發 incident_parse_error

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/src/models/incident.py

@@ -25,7 +25,7 @@ from enum import Enum
 from typing import Literal
 from uuid import UUID, uuid4
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, field_validator
 
 # 復用現有模型 (避免重複定義)
 from src.models.approval import BlastRadius
@@ -419,6 +419,14 @@ class Incident(BaseModel):
 
     # [首席架構師] 移除 json_encoders (Pydantic v2 已 deprecated)，原生序列化輸出格式與 .isoformat() 一致 v1.1 2026-04-01 Asia/Taipei
 
+    # 2026-04-01 Claude Code: 舊 Redis 資料相容性 - outcome 可能存為字串 "resolved"
+    @field_validator("outcome", mode="before")
+    @classmethod
+    def coerce_outcome_string(cls, v: object) -> object:
+        if isinstance(v, str):
+            return None  # 舊格式字串無法還原為 IncidentOutcome，捨棄即可
+        return v
+
 
 # =============================================================================
 # DTOs (Data Transfer Objects)