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/approval_execution.py

@@ -261,14 +261,25 @@ class ApprovalExecutionService:
                 self._trigger_playbook_extraction(approval)
             )
 
-            # ADR-030 Phase 5: 觸發學習服務 (fire-and-forget)
-            asyncio.create_task(
-                self._trigger_learning(
-                    approval=approval,
-                    success=True,
-                    duration_seconds=result.duration_ms / 1000 if result.duration_ms else 0,
+            # ADR-030 Phase 5 / ADR-083 Phase 3: 觸發學習服務
+            # Phase 3 修復：移除 fire-and-forget，改用 await + 30s 熔斷
+            # 超時 → 記錄 metric，主流程繼續（不 crash）
+            # 2026-04-15 ogt + Claude Sonnet 4.6（亞太）: Phase 3 fire-and-forget 修復
+            try:
+                await asyncio.wait_for(
+                    self._trigger_learning(
+                        approval=approval,
+                        success=True,
+                        duration_seconds=result.duration_ms / 1000 if result.duration_ms else 0,
+                    ),
+                    timeout=30.0,
+                )
+            except asyncio.TimeoutError:
+                logger.warning(
+                    "learning_trigger_timeout",
+                    approval_id=str(approval.id),
+                    timeout_sec=30.0,
                 )
-            )
 
             # ADR-081 Phase 1: 執行後驗證 (fire-and-forget)
             # PostExecutionVerifier 等待 K8s 收斂後抓取後狀態，補填 EvidenceSnapshot
@@ -349,15 +360,25 @@ class ApprovalExecutionService:
                 )
             )
 
-            # ADR-030 Phase 5: 觸發學習服務 (失敗案例)
-            asyncio.create_task(
-                self._trigger_learning(
-                    approval=approval,
-                    success=False,
-                    error_message=result.error,
-                    duration_seconds=result.duration_ms / 1000 if result.duration_ms else 0,
+            # ADR-030 Phase 5 / ADR-083 Phase 3: 觸發學習服務（失敗案例）
+            # Phase 3 修復：fire-and-forget → await + 30s 熔斷
+            # 2026-04-15 ogt + Claude Sonnet 4.6（亞太）: Phase 3 fire-and-forget 修復
+            try:
+                await asyncio.wait_for(
+                    self._trigger_learning(
+                        approval=approval,
+                        success=False,
+                        error_message=result.error,
+                        duration_seconds=result.duration_ms / 1000 if result.duration_ms else 0,
+                    ),
+                    timeout=30.0,
+                )
+            except asyncio.TimeoutError:
+                logger.warning(
+                    "learning_trigger_timeout",
+                    approval_id=str(approval.id),
+                    timeout_sec=30.0,
                 )
-            )
 
     async def _push_execution_result_to_alert(
         self,