Bifrost Unauthorized Channel Commission Attribution Allows Commission Diversion

The `vtoken-minting` and `slpx` pallets in Bifrost contain an improper authorization vulnerability in channel commission attribution. A signed account can supply an arbitrary registered `channel_id` when minting tokens without verifying that the caller is authorized to mint on behalf of that channel. This allows an attacker to inflate a channel's recorded mint volume and cause protocol commission payments to be disproportionately distributed to that channel during commission settlement.