fix: prevent crash when duplicating Buzz Event

[UmakanthKaspa]

Summary

• Duplicating a published Buzz Event crashed with UniqueValidationError because the unique route field
  was copied as-is
• Events with the same title also crashed on save since they generated identical routes

Changes

• Added no_copy: 1 to the route field so duplicates start with a blank route
• Used append_number_if_name_exists to auto-add -1, -2 etc. when a route already exists