Add full integration for stock supplier pickup lines into the collection pool workflow:
- Add two idempotent database migrations for stock line drv_id and state tracking
- Update stock purchase number format to POyyMMddNNSTK convention
- Extend collection pool to load both customer order items and stock purchase items
- Add stock-specific UI, driver assignment flow, and mark collected action
- Update type definitions and service logic for stock purchases and line items
- Add comprehensive test coverage for all new workflows
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