Add complete stock purchase order workflow including:
- Status tracking with sending/mail_failed states and UI labels
- Server-side PDF rendering and document storage
- File proxy API support for stock PO attachments
- Send outcome webhook callback for email notifications
Add driver app support:
- Unified stop list API for both customer deliveries and stock pickups
- Status update endpoint for collected quantities and problem reporting
- Collection map page support for stock pickup locations
Include matching PocketBase migrations, type definitions, and stock inventory fulfillment logic.
