test: migrate backend suites to pytest with module coverage gate

Split backend tests into unit and integration suites, add isolated fixtures and coverage enforcement, and update CI and test documentation. Cover current authentication, content, notification, payment, media, and admin flows; fix behaviors revealed by the new tests. Validate both suites and the per-module gate against local PostgreSQL.

apps/blog/api/schemas.py

@@ -13,9 +13,9 @@ class CategorySchema(ModelSchema):
     created_at: Optional[datetime] = None
     parent_id: Optional[int] = None
 
-    class Config:
+    class Meta:
         model = Category
-        model_fields = ["id", "name", "slug", "description", "created_at"]
+        fields = ["id", "name", "slug", "description", "created_at"]
 
     @staticmethod
     def resolve_parent_id(obj):
@@ -55,9 +55,9 @@ class CategoryFilterSchema(Schema):
 class TagSchema(ModelSchema):
     created_at: Optional[datetime] = None
 
-    class Config:
+    class Meta:
         model = Tag
-        model_fields = ["id", "name", "slug", "created_at"]
+        fields = ["id", "name", "slug", "created_at"]
 
 
 class AdminTagSchema(TagSchema):
@@ -119,9 +119,9 @@ class PostAssetSchema(ModelSchema):
     markdown_link: Optional[str] = None
     uploaded_by: AuthorSchema
 
-    class Config:
+    class Meta:
         model = PostAsset
-        model_fields = [
+        fields = [
             "id",
             "file_type",
             "title",
@@ -301,9 +301,9 @@ class CommentSchema(ModelSchema):
     deleted_at: Optional[datetime] = None
     hidden_replies_count: int = 0
 
-    class Config:
+    class Meta:
         model = Comment
-        model_fields = ["id", "content", "created_at", "updated_at", "is_approved", "hidden_at"]
+        fields = ["id", "content", "created_at", "updated_at", "is_approved", "hidden_at"]
 
     @staticmethod
     def resolve_post_id(obj):
@@ -359,9 +359,9 @@ class BlogProfileActivitySchema(Schema):
 class BlogBannerSchema(ModelSchema):
     image_url: str
 
-    class Config:
+    class Meta:
         model = BlogBanner
-        model_fields = ["id", "title", "alt_text", "url", "sort_order"]
+        fields = ["id", "title", "alt_text", "url", "sort_order"]
 
     @staticmethod
     def resolve_image_url(obj, context):