feat(backthink): 事件驱动主动消息绕过PushGate——IoT等事件该发就发(heartbeat仍受60min节流)

- trigger.go: 新增 TriggerKind(TriggerHeartbeat/TriggerEvent) + Trigger.Kind 标记触发来源
- push.go: PushRequest.TriggerKind 分流——event 跳过 gate.Allow/RecordPush(该发就发)，heartbeat 仍受 60min≤1/冷却/分类限频；PushResult.Bypassed 标记 + detail=event_bypass 区分
- backthink.go: think() 传 TriggerKind + 过同事件去重门
- event_dedup.go(新): 同事件(Source+Summary)去重防刷，无 60min 节流；不同事件/心跳后重置链
- 测试: event 连续 3 次全推 bypass / heartbeat 第2次 rate_limited / event 不消耗心跳限 / 同事件去重
- build/vet/test 全绿 + windows/darwin 交叉编译通过

internal/services/backthink/event_dedup.go

@@ -0,0 +1,31 @@
+package backthink
+
+// eventRedundant reports whether tr is a duplicate of the immediately preceding
+// event-driven push (same source + summary), so a repeating device/reminder event
+// does not spam the owner (防刷). It is the one guard that still applies to an
+// event-driven push while the PushGate itself is bypassed for events (owner
+// mandate: "该发就发" — a genuine event goes out, only a true duplicate is held).
+//
+// It atomically records tr as the latest event key when the push proceeds, and
+// clears the key on any non-event push (heartbeat) so a later repeat of a prior
+// event is not spuriously suppressed by an intervening reflection.
+//
+// The caller runs it before handing the push to the Pusher; a true duplicate is
+// recorded as suppressed (RouteNone) rather than delivered.
+func (b *Backthink) eventRedundant(tr Trigger) bool {
+	if tr.Kind != TriggerEvent {
+		// A non-event push (heartbeat) breaks the same-event chain.
+		b.eventMu.Lock()
+		b.lastEventKey = ""
+		b.eventMu.Unlock()
+		return false
+	}
+	key := tr.Source + "\x00" + tr.Summary
+	b.eventMu.Lock()
+	defer b.eventMu.Unlock()
+	if b.lastEventKey == key {
+		return true
+	}
+	b.lastEventKey = key
+	return false
+}