refactor(api): Phase 22 技術債修復 - 業務邏輯分層

P2.3: LearningService.get_learning_summary() 業務邏輯移至 Service 層
- Repository 只提供原始統計數據
- Service 計算 best_action 和 learning_status

P2.6: Playbook similarity 計算邏輯抽取
- 新增 src/utils/similarity.py
- Repository 從 utils 導入，不再定義演算法

2026-03-31 Claude Code (首席架構師技術債修復)

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

apps/api/src/services/learning_service.py

@@ -655,7 +655,12 @@ class LearningService:
         """
         取得學習摘要
 
-        2026-03-29 P0 修正: 委託 Repository 實作
+        Phase 22 P2: 業務邏輯移至 Service 層
+        2026-03-31 Claude Code (首席架構師技術債修復)
+
+        邏輯:
+        - 從 Repository 取得原始統計數據
+        - 在 Service 層計算 best_action 和 learning_status
 
         Returns:
             {
@@ -667,7 +672,51 @@ class LearningService:
                 'learning_status': 'sufficient',
             }
         """
-        return await self._repository.get_learning_summary(anomaly_key)
+        # 從 Repository 取得原始統計
+        all_stats = await self._repository.get_all_repair_stats(anomaly_key)
+
+        if not all_stats:
+            return {
+                "anomaly_key": anomaly_key,
+                "total_repair_attempts": 0,
+                "overall_success_rate": 0.0,
+                "actions_tried": [],
+                "best_action": None,
+                "learning_status": "insufficient",
+            }
+
+        # === 以下為業務邏輯，應在 Service 層 ===
+
+        total_attempts = sum(s["total"] for s in all_stats.values())
+        total_success = sum(s["success"] for s in all_stats.values())
+        overall_rate = total_success / total_attempts if total_attempts > 0 else 0.0
+
+        # 找出最佳動作 (需要至少 3 次數據)
+        best_action = None
+        best_rate = 0.0
+        for action, stats in all_stats.items():
+            if stats["total"] >= 3 and stats["success_rate"] > best_rate:
+                best_rate = stats["success_rate"]
+                best_action = {"action": action, "success_rate": best_rate}
+
+        # 判斷學習狀態
+        if total_attempts < 3:
+            learning_status = "insufficient"
+        elif total_attempts < 10:
+            learning_status = "learning"
+        elif overall_rate >= 0.8:
+            learning_status = "excellent"
+        else:
+            learning_status = "sufficient"
+
+        return {
+            "anomaly_key": anomaly_key,
+            "total_repair_attempts": total_attempts,
+            "overall_success_rate": overall_rate,
+            "actions_tried": list(all_stats.keys()),
+            "best_action": best_action,
+            "learning_status": learning_status,
+        }
 
     def _get_action_tier(self, action: str) -> int:
         """取得動作的 Tier"""