feat(moderation): add chat bans list endpoint with admin access checks

app/chats/service.py

@@ -7,6 +7,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from app.chats import repository
 from app.chats.models import Chat, ChatMember, ChatMemberRole, ChatType
 from app.chats.schemas import (
+    ChatBanRead,
     ChatCreateRequest,
     ChatDeleteRequest,
     ChatDiscoverRead,
@@ -471,6 +472,28 @@ async def unban_chat_member_for_user(
     await db.commit()
 
 
+async def list_chat_bans_for_user(
+    db: AsyncSession,
+    *,
+    chat_id: int,
+    actor_user_id: int,
+) -> list[ChatBanRead]:
+    chat, actor_membership = await _get_chat_and_membership(db, chat_id=chat_id, user_id=actor_user_id)
+    _ensure_group_or_channel(chat.type)
+    if actor_membership.role not in {ChatMemberRole.OWNER, ChatMemberRole.ADMIN}:
+        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Insufficient permissions")
+    bans = await repository.list_chat_bans(db, chat_id=chat_id)
+    return [
+        ChatBanRead(
+            chat_id=ban.chat_id,
+            user_id=ban.user_id,
+            banned_by_user_id=ban.banned_by_user_id,
+            created_at=ban.created_at,
+        )
+        for ban in bans
+    ]
+
+
 async def leave_chat_for_user(db: AsyncSession, *, chat_id: int, user_id: int) -> None:
     chat, membership = await _get_chat_and_membership(db, chat_id=chat_id, user_id=user_id)
     _ensure_group_or_channel(chat.type)