feat(alert): 统一告警出口 TG bot + runbook [tsk_9YMHMTfWJyNB]

新增 server/internal/alert 包（15G）：
- 定义 Notifier 接口及 7 种 EventType（判封确认/补新失败/水位低/熔断/
  探针失联/心跳缺失/故障态）
- TGNotifier：Bot API 发送，Critical 事件不去重，Warning/Info 事件
  10min SETNX 去重窗口，失败重试 ≤2 次后降级至 LogNotifier
- LogNotifier：slog 结构化降级实现
- 单测：7 种事件模板 + runbook 锚点正确性；去重窗口内第二条被抑制；
  TG 5xx 重试后 fallback 且 Notify() 返回 nil；
  runbook 文件锚点与枚举一致性

接入 scheduler（替换旧的 NotifyFault 桩）：
- detect/engine.go：故障态（Rule 5）→ EventTypeFault；
  判封确认（Rule 3）→ EventTypeBlockConfirmed
- orchestrate/deps.go：Notifier 类型别名指向 alert.Notifier
- orchestrate/replacer.go：补新失败 → EventTypeReplenishFailed；
  熔断触发 → EventTypeBreakerTripped
- probe/prober_agent.go：failCount ≥3 → EventTypeProbeAgentLost
- probe/store.go：新增 CheckHeartbeats() 供 15H 检测心跳缺失>90s

新增 docs/runbook-scheduler.md：7 节各含含义/先查什么/处置/升级条件，
锚点与代码枚举对应。

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

server/internal/scheduler/orchestrate/deps.go

@@ -8,9 +8,9 @@ package orchestrate
 
 import (
 	"context"
-	"log/slog"
 	"time"
 
+	"github.com/wangjia/pangolin/server/internal/alert"
 	"github.com/wangjia/pangolin/server/internal/scheduler/probe"
 )
 
@@ -164,25 +164,17 @@ func (StubBreaker) Allow(_, _ string) bool { return true }
 func (StubBreaker) Record(_, _ string) {}
 
 // ─────────────────────────────────────────────────────────────────────────────
-// Notifier (15G stub)
+// Notifier (15G)
 // ─────────────────────────────────────────────────────────────────────────────
 
-// Notifier is the 15G alerting interface.
-type Notifier interface {
-	NotifyFault(ctx context.Context, nodeID, reason string) error
-}
+// Notifier is the 15G unified alert outlet used by the orchestrator.
+// It is satisfied by alert.Notifier (TG implementation) and alert.LogNotifier
+// (fallback / development stub).
+type Notifier = alert.Notifier
 
-// LogNotifier logs faults via slog. Used when no real notifier is wired.
-type LogNotifier struct{}
-
-// NotifyFault implements Notifier.
-func (LogNotifier) NotifyFault(_ context.Context, nodeID, reason string) error {
-	slog.Warn("orchestrate: replacement failed — manual review required",
-		"node_id", nodeID,
-		"reason", reason,
-	)
-	return nil
-}
+// LogNotifier is re-exported for callers that need a no-op Notifier without
+// importing the alert package directly.
+type LogNotifier = alert.LogNotifier
 
 // ─────────────────────────────────────────────────────────────────────────────
 // Clock (for testability)