feat(contacts): add contacts module with backend APIs and web tab

- add user_contacts table and migration

- expose /users/contacts list/add/remove endpoints

- add Contacts tab in chat list with add/remove actions

app/database/models.py

@@ -4,7 +4,7 @@ from app.email.models import EmailLog
 from app.media.models import Attachment
 from app.messages.models import Message, MessageHidden, MessageIdempotencyKey, MessageReaction, MessageReceipt
 from app.notifications.models import NotificationLog
-from app.users.models import User
+from app.users.models import User, UserContact
 
 __all__ = [
     "Attachment",
@@ -21,4 +21,5 @@ __all__ = [
     "NotificationLog",
     "PasswordResetToken",
     "User",
+    "UserContact",
 ]