Advanced product endpoints

Additional routes for sourcing workflows (1688-heavy unless noted). Overview: Products.

Endpoint index

Method	Path	Purpose
GET	/v1/products/channels	Per-channel capability flags
POST	/v1/products/freight/estimate	Domestic shipping — same body as order preview; returns freight in fen
POST	/v1/products/batch-check	Taobao mapping debug (create auto-checks batch)
POST	/v1/products/top-keywords	1688 category hot keywords
POST	/v1/products/top-list	1688 ranked product lists
POST	/v1/products/daily-sales-trend	1688 daily sales trend (max 90 days)

Upstream response format {#upstream-format}

Add "response_format": "upstream" to return vendor JSON in an upstream envelope instead of standard models. See Response format.