feat(aiops): capacity_forecaster — Phase 4 Holt-Winters MVP (predict_linear)

統帥批准 4 項下階段候選之一完成: AI 容量預測.

新增 capacity_forecaster_job.py (~220 行):
  每日 05:00 Taipei 跑預測 (02:00 scanner → 03:00 compliance →
  04:00 Hermes → 05:00 forecaster 形成完整日鏈).

預測方法論 (MVP):
  Prometheus predict_linear(metric[7d], 86400*7) — 基於過去 7d 做線性外推
  3 個預測 query:
    1. disk_saturation_7d: predict_linear(node_filesystem_avail_bytes[7d], 7d) < 0
    2. mem_saturation_7d: predict_linear(MemAvailable[7d], 7d) / MemTotal < 10%
    3. cpu_high_7d_trend: avg_over_time(cpu_used_pct[7d]) > 70%

發現高風險 host → 寫 aol(capacity_recommendation) + 推 Telegram
  - input: host + horizon + findings count
  - output: findings list + proposed_actions + requires_human_decision=true

proposed_actions 依 findings 推導:
  - disk: 清理 log/docker/PG WAL 或擴容
  - mem: top consumer / JVM 調整
  - cpu: scale out / vCPU 擴充

統帥鐵律對齊:
  ✅ 只推建議不自動 scale up
  ✅ 7d window 有足夠樣本
  ✅ AI 預測 + 人工決策

未來 TODO:
  - 真 Holt-Winters (含季節性) — 需 Python statsmodels
  - 業務週期調整 (週一高峰/週末低谷)

Wire main.py lifespan asyncio.create_task()

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/api/src/main.py

@@ -450,6 +450,16 @@ async def lifespan(_app: FastAPI) -> AsyncGenerator[None, None]:
     except Exception as e:
         logger.warning("hermes_rule_quality_loop_schedule_failed", error=str(e))
 
+    # ADR-090 § Phase 4 Capacity Forecaster (2026-04-19 ogt + Claude Opus 4.7 Asia/Taipei)
+    # 每日 05:00 Taipei 用 Prometheus predict_linear 預測未來 7d disk/mem/cpu 飽和
+    # 高風險 host 寫 aol(capacity_recommendation) + Telegram 建議
+    try:
+        from src.jobs.capacity_forecaster_job import run_capacity_forecaster_loop
+        asyncio.create_task(run_capacity_forecaster_loop())
+        logger.info("capacity_forecaster_loop_scheduled", daily_trigger_hour_taipei=5)
+    except Exception as e:
+        logger.warning("capacity_forecaster_loop_schedule_failed", error=str(e))
+
     # ADR-076 Task 4: 每日 08:00 台北時間自動日度巡檢報告
     # 2026-04-14 Claude Haiku 4.5 Asia/Taipei
     try: