* [docs] Update agent-network docs for management-owned pricing
The docs still described the retired proxy-side pricing: pricing.Loader,
pricing_path, MiddlewareDataDir, embedded defaults_pricing.yaml, and the
symlink-safe Unix loader. Rewrite them for the current design — management
synthesizes the whole table and ships it in cost_meter's ConfigJSON, so the
proxy carries no price list and has nothing to reload.