feat: dedup expected data by handover_no before export submit

- store.get_existing_handover_nos: query PG expected_record.handover_no

- inject dedup skip before submitting export in zto/yunda/anneng/shunxin

- shunxin reads RTS handover_no from waybill-list view (method 1)

- force-redownload switch threaded via task_spec -> dispatch -> impl

- schema: add idx_expected_handover index

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

schema.sql

@@ -24,6 +24,7 @@ CREATE TABLE IF NOT EXISTS expected_record (
     UNIQUE (site, waybill_no)
 );
 CREATE INDEX IF NOT EXISTS idx_expected_site_date ON expected_record (site, business_date);
+CREATE INDEX IF NOT EXISTS idx_expected_handover ON expected_record (site, handover_no);
 
 -- 实到货物（扫描件级：一扫描一行；每扫描一件系统生成一个单号）
 CREATE TABLE IF NOT EXISTS actual_record (