feat: add comments feature with nested replies and recursive rendering

Implement full comments system: domain entities (Comment, CommentLike),
value objects (CommentContent), use cases (CRUD, like toggle), SQLAlchemy
repository, API v1 endpoints, web UI with comment form and nested replies,
i18n translations (EN/RU/FR/DE), and E2E tests.

Fix nested reply (reply-to-reply) not displaying — the flat reply_comments
dict was only queried for top-level comment IDs, so deeply nested replies
were saved to DB (incrementing comment count) but never rendered. Switch
to a recursive Jinja2 macro that renders any nesting depth.

app/infrastructure/di/providers.py

@@ -10,19 +10,24 @@ from dishka import Provider, Scope, provide
 from sqlalchemy.ext.asyncio import AsyncEngine, AsyncSession
 
 from app.application import (
+    CreateCommentUseCase,
     CreatePostUseCase,
+    DeleteCommentUseCase,
     DeletePostUseCase,
     GetPostUseCase,
+    ListCommentsUseCase,
     ListPostsUseCase,
     PublishPostUseCase,
+    ToggleCommentLikeUseCase,
     TogglePostLikeUseCase,
     UpdatePostUseCase,
 )
 from app.application.interfaces import TransactionManager
-from app.domain.repositories import PostRepository
+from app.domain.repositories import CommentRepository, PostRepository
 from app.infrastructure.auth import KeycloakAuthClient, MockKeycloakClient
 from app.infrastructure.config.settings import settings
 from app.infrastructure.database.connection import AsyncSessionLocal, engine
+from app.infrastructure.repositories.comment import SQLAlchemyCommentRepository
 from app.infrastructure.repositories.post import SQLAlchemyPostRepository
 
 
@@ -81,6 +86,18 @@ class RepositoryProvider(Provider):
         """
         return SQLAlchemyPostRepository(session)
 
+    @provide(scope=Scope.REQUEST)
+    def get_comment_repository(self, session: AsyncSession) -> CommentRepository:
+        """Provide CommentRepository implementation.
+
+        Args:
+            session: Database session from DI container.
+
+        Returns:
+            SQLAlchemyCommentRepository instance.
+        """
+        return SQLAlchemyCommentRepository(session)
+
 
 class TransactionManagerProvider(Provider):
     """Provider for transaction manager.
@@ -257,6 +274,86 @@ class UseCaseProvider(Provider):
             tx_manager=tx_manager,
         )
 
+    @provide(scope=Scope.REQUEST)
+    def get_create_comment_use_case(
+        self,
+        post_repo: PostRepository,
+        comment_repo: CommentRepository,
+        tx_manager: TransactionManager,
+    ) -> CreateCommentUseCase:
+        """Provide CreateCommentUseCase.
+
+        Args:
+            post_repo: Post repository dependency.
+            comment_repo: Comment repository dependency.
+            tx_manager: Transaction manager dependency.
+
+        Returns:
+            Configured CreateCommentUseCase instance.
+        """
+        return CreateCommentUseCase(
+            post_repo=post_repo,
+            comment_repo=comment_repo,
+            tx_manager=tx_manager,
+        )
+
+    @provide(scope=Scope.REQUEST)
+    def get_list_comments_use_case(
+        self,
+        comment_repo: CommentRepository,
+    ) -> ListCommentsUseCase:
+        """Provide ListCommentsUseCase.
+
+        Args:
+            comment_repo: Comment repository dependency.
+
+        Returns:
+            Configured ListCommentsUseCase instance.
+        """
+        return ListCommentsUseCase(
+            comment_repo=comment_repo,
+        )
+
+    @provide(scope=Scope.REQUEST)
+    def get_delete_comment_use_case(
+        self,
+        comment_repo: CommentRepository,
+        tx_manager: TransactionManager,
+    ) -> DeleteCommentUseCase:
+        """Provide DeleteCommentUseCase.
+
+        Args:
+            comment_repo: Comment repository dependency.
+            tx_manager: Transaction manager dependency.
+
+        Returns:
+            Configured DeleteCommentUseCase instance.
+        """
+        return DeleteCommentUseCase(
+            comment_repo=comment_repo,
+            tx_manager=tx_manager,
+        )
+
+    @provide(scope=Scope.REQUEST)
+    def get_toggle_comment_like_use_case(
+        self,
+        comment_repo: CommentRepository,
+        tx_manager: TransactionManager,
+    ) -> ToggleCommentLikeUseCase:
+        """Provide ToggleCommentLikeUseCase.
+
+        Args:
+            comment_repo: Comment repository dependency.
+            tx_manager: Transaction manager dependency.
+
+        Returns:
+            Configured ToggleCommentLikeUseCase instance.
+        """
+        return ToggleCommentLikeUseCase(
+            comment_repo=comment_repo,
+            tx_manager=tx_manager,
+        )
+
 
 class KeycloakProvider(Provider):
     """Provider for Keycloak authentication client.