Fixes: 1) Validate gateway presence in `process_transaction_changes` signal; 2) Add missing imports for `Type`, `create_object`, and `AbstractGateway`;
Extra: 1) Cleanup unused diff lines in migrations files; 2) Improve JSONField, FloatField, and PositiveIntegerField declarations by consolidating into single lines; 3) Remove redundant match-case logic in `signals.py`.
Fixes: 1) Correct import order in `payments.admin`.
Extra: 1) Update `productimage.priority` field in `core` app with default value and help text; 2) Include `integration_path` in `Vendor` admin additional fields.
Fixes: 1) Fix shebangs in Docker entry-point scripts to use `/usr/bin/bash`.
Extra: 1) Refactor slug fields in `core` migrations for `Brand`, `Category`, and `Product`; 2) Cleanup and simplify admin code in `core/admin.py`.
Updated the API version from 2.5.0 to 2.6.0 in the DRF settings for consistency across configurations. Reformatted migration files for better readability, ensuring consistency in code style and improving maintainability. These changes do not alter functionality but enhance clarity and documentation.
