feat(learning): 實作 Playbook 信心度調整機制 (ADR-030)

- 新增 _promote_playbook: 高評分提升信心度 +0.1
- 新增 _demote_playbook: 低評分降低信心度 -0.15
- 新增 find_by_source_incident: 按 incident_id 查詢 Playbook
- 新增 adjust_confidence: 信心度調整 + 狀態自動轉換
- 新增 Playbook.failure_rate 屬性

自動狀態轉換:
- ai_confidence >= 0.9 + DRAFT → 自動 APPROVED
- ai_confidence < 0.3 + failure_rate > 50% → 自動 DEPRECATED

測試: 13 案例全部通過

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

apps/api/src/repositories/interfaces.py

@@ -244,6 +244,39 @@ class IPlaybookRepository(Protocol):
         """更新執行統計"""
         ...
 
+    async def find_by_source_incident(
+        self,
+        incident_id: str,
+    ) -> list[Playbook]:
+        """
+        根據來源 Incident ID 找 Playbook
+
+        2026-03-30 Claude Code: Learning Service 信心度調整用
+        尋找 source_incident_ids 包含此 incident_id 的 Playbooks
+        """
+        ...
+
+    async def adjust_confidence(
+        self,
+        playbook_id: str,
+        delta: float,
+        reason: str,
+    ) -> Playbook | None:
+        """
+        調整 Playbook 信心度
+
+        2026-03-30 Claude Code: Learning Service 信心度調整用
+
+        Args:
+            playbook_id: Playbook ID
+            delta: 調整量 (+/- 0.0~1.0)
+            reason: 調整原因 (審計用)
+
+        Returns:
+            更新後的 Playbook，或 None (如果不存在)
+        """
+        ...
+
 
 @runtime_checkable
 class ILearningRepository(Protocol):