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/gateway/extra_test.go

@@ -1526,7 +1526,9 @@ func TestAdminRagEmptyWhenUnwired(t *testing.T) {
 	}
 }
 
-func TestAdminRagDeleteNotImplemented(t *testing.T) {
+// TestAdminRagDeleteUnsupportedStore501 asserts a store that cannot delete is
+// answered with an honest 501 rather than a fabricated success.
+func TestAdminRagDeleteUnsupportedStore501(t *testing.T) {
 	t.Parallel()
 	srv, ts, jwt := buildEnv(t, cfgDefault(), Deps{RAG: &stubRag{err: knowledge.ErrWriteUnsupported}})
 	_ = srv
@@ -1537,8 +1539,8 @@ func TestAdminRagDeleteNotImplemented(t *testing.T) {
 		t.Fatalf("status = %d, want 501 (body=%s)", resp.StatusCode, body)
 	}
 	wantErrorShape(t, body)
-	if !strings.Contains(string(body), "M10") {
-		t.Fatalf("error body = %s, want M10 write message", body)
+	if !strings.Contains(string(body), "not_implemented") {
+		t.Fatalf("error body = %s, want not_implemented code", body)
 	}
 }