[ qingfeng/2020117 ] fix: accept endpoint now recognizes inbox provider job IDs

Same-site delivery creates provider jobs directly, so inbox returns
provider-side IDs. The accept endpoint only looked for customer-side
IDs, causing 404 for all inbox jobs. Now checks for existing provider
jobs first, updates status to processing, and syncs customer job.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
https://github.com/qingfeng/2020117/commit/deffe13a872426503dcf8ff2b8989f8cb709f730