feat(plutus): plutus_mint module — Plutus-policy mint with custom output

Adds aldabra-core::plutus_mint with build_signed_plutus_mint and
build_unsigned_plutus_mint. Designed for Agora-style DAO bringup
where every "mint a single ST token under a Plutus policy and
deposit it at a script address with inline datum" tx shares the
same shape (governor / stake / proposal bootstrap).

PlutusMintArgs takes:
- required_inputs: UTxOs that MUST be spent (e.g. gstOutRef the
  GST policy is parameterized on)
- policy_cbor + policy_version + redeemer + ex_units
- mint_assets: list of (asset_name_hex, qty) under this policy
- dest_address + dest_lovelace + dest_extra_assets to forward
  + optional inline datum

Same collateral/funding pattern as plutus.rs::build_signed_plutus_spend
(smallest ADA-only ≥ 5 ADA for collateral, separate funding picks
to cover dest + fee + min_change). PlutusV3 cost-model wired into
language_view per the existing PLUTUS-4 fix.

3 unit tests cover empty-policy / empty-mint / required-input-not-
in-available rejections + the governor-bootstrap shape produces
valid Conway CBOR.

This is Phase 2 of the Track B-fast preprod DAO bringup. Together
with the wallet-ref-script Phase 1 commits (8b0e090 + a1060b1)
it gives aldabra everything needed to deploy 11 Agora script ref
UTxOs + bootstrap a governor + bootstrap stakes on preprod.

crates/aldabra-core/src/lib.rs

@@ -43,6 +43,7 @@ pub mod metadata;
 pub mod mint;
 pub mod plutus;
 pub mod plutus_cost_models;
+pub mod plutus_mint;
 pub mod sign;
 pub mod stake;
 pub mod tx;
@@ -62,6 +63,10 @@ pub use plutus::{
     build_signed_plutus_spend, looks_like_script_address, PlutusExUnits, PlutusInput,
     PlutusVersion, DEFAULT_EX_UNITS, MIN_COLLATERAL_LOVELACE,
 };
+pub use plutus_mint::{
+    build_signed_plutus_mint, build_unsigned_plutus_mint, ExtraDestAsset, PlutusMintArgs,
+    PlutusMintAsset,
+};
 pub use stake::{build_signed_stake_delegation, parse_pool_id, STAKE_KEY_DEPOSIT_LOVELACE};
 pub use governance::{
     build_signed_drep_deregistration, build_signed_drep_registration,