fix(incidents): GET /incidents 加 48h age filter，阻止舊 incident 反覆觸發 AI 分析

根本原因: DECISION_TOKEN_TTL=3600s → 舊 incident token 每小時過期
→ GET /api/v1/incidents 重複觸發 get_or_create_decision → OPENCLAW_NEMO timeout
→ Expert System fallback (confidence=20%) → Telegram 洪水

修復: 只對 created_at 在 48h 內的 incident 觸發背景 AI 分析
48h+ 的舊 incident 不再觸發（仍顯示在列表，只是不重新分析）

2026-04-16 Claude Sonnet 4.6 Asia/Taipei

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

apps/api/src/api/v1/incidents.py

@@ -166,10 +166,20 @@ async def list_incidents() -> IncidentListResponse:
                 else:
                     # 無快取 → 背景觸發，本次返回 None（前端看到 decision=null 會 poll）
                     responses.append(IncidentResponse.from_incident(incident, None))
-                    timeout = 120.0 if incident.severity in (Severity.P0, Severity.P1) else 180.0
-                    background_tasks.append(
-                        decision_manager.get_or_create_decision(incident=incident, timeout_sec=timeout)
-                    )
+                    # 2026-04-16 Claude Sonnet 4.6: 只對 48h 內的 incident 觸發 AI 分析
+                    # 舊 incident token 每小時過期，若不限制會反覆重新分析歷史事件 → Telegram 洪水
+                    from datetime import datetime, timezone, timedelta
+                    _created = getattr(incident, "created_at", None)
+                    _too_old = False
+                    if _created:
+                        if _created.tzinfo is None:
+                            _created = _created.replace(tzinfo=timezone.utc)
+                        _too_old = (_created < datetime.now(timezone.utc) - timedelta(hours=48))
+                    if not _too_old:
+                        timeout = 120.0 if incident.severity in (Severity.P0, Severity.P1) else 180.0
+                        background_tasks.append(
+                            decision_manager.get_or_create_decision(incident=incident, timeout_sec=timeout)
+                        )
             except Exception as e:
                 logger.warning(
                     "decision_generation_failed",