[REF] Code quality improvements and structure fixes

- Add mypy.ini configuration to exclude migration scripts
- Rename migration files to proper snake_case (post-migration.py → post_migration.py)
- Add __init__.py to migration directories for proper Python package structure
- Add new portal access tests for website_sale_aplicoop
- Code formatting improvements (black, isort)
- Update copilot instructions and project configuration

Related to previous code quality refactoring work.

website_sale_aplicoop/tests/test_group_order.py

@@ -4,7 +4,7 @@
 from datetime import datetime
 from datetime import timedelta
 
-from psycopg2 import IntegrityError
+from psycopg2 import IntegrityError  # noqa: F401
 
 from odoo import fields
 from odoo.exceptions import ValidationError