feat: Iteration 3 — 咨询轮询、统计概览、埋点后端

- consultation_service 支持 after_id 增量消息查询
- 小程序咨询详情页 8 秒轮询新消息
- 新增 DashboardStatsResp 综合统计端点 (/statistics/dashboard)
- 新增 /analytics/batch 埋点接收端点（日志记录模式）

crates/erp-server/src/main.rs

@@ -494,6 +494,10 @@ async fn main() -> anyhow::Result<()> {
             "/docs/openapi.json",
             axum::routing::get(handlers::openapi::openapi_spec),
         )
+        .route(
+            "/analytics/batch",
+            axum::routing::post(handlers::analytics::batch),
+        )
         .layer(axum::middleware::from_fn_with_state(
             state.clone(),
             middleware::rate_limit::rate_limit_by_ip,