Derive Macro ArkheEvent 

#[derive(ArkheEvent)]
{
    // Attributes available to this derive:
    #[arkhe]
}

Re-export of the kernel-companion derive macros. ArkheAction emits Sealed + ActionDeriv (pair with impl ActionCompute). ArkheComponent and ArkheEvent emit Sealed + the corresponding kernel trait — postcard-canonical defaults handle the byte round trip. Every derive expects #[arkhe(type_code = N, schema_version = M)]. Derive Sealed + Event. Same shape as ArkheComponent; the user type must additionally derive Debug plus serde.