[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_edge_cases.py

@@ -18,7 +18,7 @@ from datetime import timedelta
 
 from dateutil.relativedelta import relativedelta
 
-from odoo.exceptions import ValidationError
+from odoo.exceptions import ValidationError  # noqa: F401
 from odoo.tests.common import TransactionCase
 
 
@@ -430,7 +430,7 @@ class TestOrderWithoutEndDate(TransactionCase):
         """Test order with end_date = NULL (ongoing order)."""
         start = date.today()
 
-        order = self.env["group.order"].create(
+        self.env["group.order"].create(
             {
                 "name": "Permanent Order",
                 "group_ids": [(6, 0, [self.group.id])],