feat(Phase 3): 學習閉環重建 — 三根因修復 + 2x EWMA + Evolver Agent

ADR-083 Phase 3 學習閉環重建：

**三根因修復**
- approval_execution.py: fire-and-forget create_task → await asyncio.wait_for(timeout=30) × 2
  （成功路徑 L265 + 失敗路徑 L353，超時記錄 learning_trigger_timeout metric，主流程不 crash）
- models/approval.py: ApprovalRequestBase 新增 matched_playbook_id 欄位
- decision_manager.py: _auto_execute 建立 ApprovalRequest 時填充 matched_playbook_id
- learning_service.py: 雙路徑查找 _matched_pb_id（matched_playbook_id + metadata fallback）

**2x EWMA 負向強化**
- models/playbook.py: 新增 trust_score: float = 0.3（EWMA 動態信任度欄位）
- repositories/playbook_repository.py: update_stats 加 EWMA
  成功: trust = 0.9 × old + 0.1 × 1.0
  失敗: trust = 0.8 × old + 0.2 × 0.0（衰減速度 2x）
  trust < 0.1 → log warning，等 Evolver 封存

**Evolver Agent（新建）**
- services/playbook_evolver.py: 三功能全靜態規則
  1. 低信任封存: trust < 0.1 → DEPRECATED
  2. 休眠封存: 30d 未使用 AND trust < 0.5 → DEPRECATED
  3. 相似合併: 症狀 Jaccard > 0.9 → 保留高 trust，封存低 trust
  AIOPS_P3_EVOLVER_ENABLED=False 預設關閉

**文件**
- ADR-083 學習閉環重建
- MASTER §8 Phase 3 完工記錄

AIOPS_P3_ENABLED=False（預設），骨架就位等統帥批准開啟

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

apps/api/src/services/learning_service.py

@@ -205,24 +205,33 @@ class LearningService:
         trust_after = trust_record.score if trust_record else 0
 
         # 2. 更新 Playbook 統計 (如果有匹配)
+        # ADR-083 Phase 3: 雙路徑查找 matched_playbook_id
+        # 路徑 A: ApprovalRequest.matched_playbook_id（auto_execute 路徑，Phase 3 修復）
+        # 路徑 B: approval.metadata["playbook_id"]（人工審核路徑，透過 proposal_service 存入 metadata）
+        # 2026-04-15 ogt + Claude Sonnet 4.6（亞太）: Phase 3 Playbook EWMA 修復
+        _matched_pb_id: str | None = (
+            getattr(approval, "matched_playbook_id", None)
+            or (approval.metadata or {}).get("matched_playbook_id")
+            or (approval.metadata or {}).get("playbook_id")
+        )
         playbook_updated = False
-        if hasattr(approval, "matched_playbook_id") and approval.matched_playbook_id:
+        if _matched_pb_id:
             try:
                 await self._update_playbook_stats(
-                    playbook_id=approval.matched_playbook_id,
+                    playbook_id=_matched_pb_id,
                     success=result.success,
                 )
                 playbook_updated = True
             except Exception as e:
                 logger.warning(
                     "playbook_stats_update_failed",
-                    playbook_id=approval.matched_playbook_id,
+                    playbook_id=_matched_pb_id,
                     error=str(e),
                 )
 
         # 3. 嘗試萃取新 Playbook (成功且無匹配 Playbook)
         new_playbook_id = None
-        if result.success and not getattr(approval, "matched_playbook_id", None):
+        if result.success and not _matched_pb_id:
             try:
                 new_playbook_id = await self._try_extract_playbook(
                     incident_id=result.incident_id,