plutus_mint: thread additional_signers into tx body's required_signers

On Babbage+, Plutus's TxInfo.signatories is populated only from the
tx body's required_signers field — vkey witnesses alone don't surface
in the script context. Without this, any Agora script that calls
pauthorizedBy/txSignedBy fails. Stake-bootstrap on preprod erred
because the owner pkh wasn't in signatories despite the wallet
signing the tx.

MCP layer always passes [wallet_pkh]; callers can append cosigner
pkhs for multi-sig flows.

crates/aldabra-mcp/src/tools.rs

@@ -1654,6 +1654,8 @@ impl WalletService {
             }
         };
 
+        let wallet_pkh = self.inner.payment_key.public_key_hash();
+        let signers = [wallet_pkh];
         let core_args = CorePlutusMintArgs {
             required_inputs: &required,
             policy_cbor: &policy_cbor,
@@ -1665,6 +1667,7 @@ impl WalletService {
             dest_lovelace,
             dest_extra_assets: &core_extras,
             dest_inline_datum_cbor: datum_bytes.as_deref(),
+            additional_signers: &signers,
         };
 
         let unsigned = build_unsigned_plutus_mint(