Refactor locale validation and update style consistency across schemas, tests, and migrations

- Replaced `SUPPORTED_LOCALES` with `supported_locales` for naming consistency.
- Applied formatting improvements to multiline statements for better readability.
- Cleaned up redundant comments and streamlined test assertions.

backend/tests/api/dependencies/test_locale_dependencies.py

@@ -67,9 +67,7 @@ class TestParseAcceptLanguage:
 
     def test_parse_complex_header(self):
         """Test complex Accept-Language header with multiple locales"""
-        result = parse_accept_language(
-            "it-IT,it;q=0.9,en-US;q=0.8,en;q=0.7,fr;q=0.6"
-        )
+        result = parse_accept_language("it-IT,it;q=0.9,en-US;q=0.8,en;q=0.7,fr;q=0.6")
         assert result == "it-it"
 
     def test_parse_whitespace_handling(self):
@@ -199,9 +197,7 @@ class TestGetLocale:
         assert result == "en"
 
     @pytest.mark.asyncio
-    async def test_locale_from_accept_language_header(
-        self, async_user_without_locale
-    ):
+    async def test_locale_from_accept_language_header(self, async_user_without_locale):
         """Test locale detection from Accept-Language header when user has no preference"""
         # Mock request with Italian Accept-Language (it-IT has highest priority)
         mock_request = MagicMock()

backend/tests/schemas/test_user_schemas.py

@@ -334,11 +334,7 @@ class TestLocaleValidation:
     def test_locale_in_user_update_with_other_fields(self):
         """Test locale validation works when combined with other fields"""
         # Valid locale with other fields
-        user = UserUpdate(
-            first_name="Mario",
-            last_name="Rossi",
-            locale="it"
-        )
+        user = UserUpdate(first_name="Mario", last_name="Rossi", locale="it")
         assert user.locale == "it"
         assert user.first_name == "Mario"
 
@@ -347,7 +343,7 @@ class TestLocaleValidation:
             UserUpdate(
                 first_name="Pierre",
                 last_name="Dupont",
-                locale="fr"  # Unsupported
+                locale="fr",  # Unsupported
             )
 
     def test_supported_locales_list(self):
@@ -357,7 +353,9 @@ class TestLocaleValidation:
         # Expected output (normalized to lowercase)
         expected_outputs = ["en", "it", "en-us", "en-gb", "it-it"]
 
-        for input_locale, expected_output in zip(input_locales, expected_outputs):
+        for input_locale, expected_output in zip(
+            input_locales, expected_outputs, strict=True
+        ):
             user = UserUpdate(locale=input_locale)
             assert user.locale == expected_output