fix: emit pre-increment nonce in CollectableMinted event and add zero-address owner check in init

- CollectableMinted event was emitting the post-increment nonce (nonce+1)
  instead of the nonce actually used for EIP-712 signature verification.
  This caused off-chain systems to see a nonce value that didn't match the
  signed payload, breaking event-to-signature correlation.

- init() validated _platformRoyaltyReceiver for zero address but not _owner.
  Since _guardInitializeOwner is not overridden, Solady's _initializeOwner
  does not guard against double-init. Passing address(0) as _owner would
  leave the protocol without an owner and the init guard bypassable.

Co-Authored-By: Xingyu Li <72717104+0xlxy@users.noreply.github.com>