feat(backthink/admin): ③b — rag/delete 真实现 + D1 推送出口钩子(自建优先→个推兜底) + api-reference 补 D2/D3/D5 补丁

- B5: POST /admin/rag/delete 真做(DeleteDocument→DeleteProject 级联删章节+索引清理, owner+审计, 200/404/500, 500降级兜底); users/iot scenarios+rules 诚实501(无用户表/IoT场景规则模型, 消息写明缺什么, 不伪造), 锁住 501+not_implemented
- D1: backthink/push_outlet.go PushExporter{Export}; pushOutlet 自建HTTP(2xx=送达, token仅Authorization头+error脱敏)优先→Getui兜底(未接入, 诚实日志'getui not integrated'+(false,nil)); backthink.Deps.Exporter → pusher.withExporter, Push 在WS/IM后 exportAsync(detached+5s超时, 失败仅日志, 不破坏现有投递, 限流不上报); config PushOutletConfig(PUSH_EXPORTER_* + GETUI_*占位)
- 前端 Rag.tsx/api.ts 删除后 reload + 类型; Docs/api-client v0.31 + api-reference(#23 owner/200-404, §8.4, 端点表PATCH/DELETE messages + pinned + messages?q=)
- 测试(push_outlet/admin_rag_delete/admin_honest501/knowledge store), 后端+前端build全绿+3平台交叉编译
- 刻意: Getui SDK 未接入(无SDK不硬造), 主人自建服务填 PUSH_EXPORTER_URL/TOKEN 即可

internal/services/backthink/sinks.go

@@ -25,10 +25,10 @@ func (b *Backthink) SetIMSink(im IMAdapter) {
 	b.rebuildPusherLocked()
 }
 
-// rebuildPusherLocked replaces the pusher from the current sinks and gate. The
-// caller must hold b.mu.
+// rebuildPusherLocked replaces the pusher from the current sinks, gate and push
+// outlet. The caller must hold b.mu.
 func (b *Backthink) rebuildPusherLocked() {
-	b.pusher = newPusher(b.deps.Active, b.deps.IM, b.gate, b.log)
+	b.pusher = newPusher(b.deps.Active, b.deps.IM, b.gate, b.log).withExporter(b.deps.Exporter)
 }
 
 // currentPusher returns the active pusher under the lifecycle lock, so a sink