feat(wallet): reference-script + extras on payment outputs

Adds Babbage/Conway-era reference-script attachment to wallet_send
and wallet_send_unsigned. The output can now carry any combination
of {native assets, inline datum, reference script}.

Why: deploying Plutus validators / minting policies as on-chain
reference UTxOs is the standard Cardano dApp pattern (Agora, Liqwid,
SundaeSwap all do this). Without it every spend or mint that uses
a script has to inline-witness the full CBOR — kilobytes per tx and
quadratic with tx size. Reference scripts let downstream txs witness
via `read_only_input` for ~32 bytes overhead.

API surface:

aldabra-core:
- new `ReferenceScriptSpec<'a> { kind: ScriptKind, cbor: &'a [u8] }`
- `ScriptKind` re-exported from pallas_txbuilder (PlutusV1/V2/V3/Native)
- new `build_signed_payment_extras(...)` and
  `build_unsigned_payment_extras(...)` — supersets of the existing
  `_with_assets` functions; take both `to_inline_datum_cbor` and
  `to_reference_script` Options
- existing `_with_assets` functions kept as thin wrappers that pass
  None for ref script — backwards compatible
- internal `output_with_assets`, `prepare_payment`, and
  `build_staging_with_fee` thread the new ref-script Option through

aldabra-mcp:
- `SendArgs` and `UnsignedSendArgs` gain
  `reference_script_cbor_hex: Option<String>` and
  `reference_script_kind: Option<String>`
- Both must be set or both omitted; mismatched returns a clean error
- `parse_script_kind` helper — case-insensitive, accepts
  PlutusV1/V2/V3/Native (plus shortcut V1/V2/V3)

Reference scripts are intentionally never attached to change outputs.
The change goes back to the wallet's own address, where a script
attachment would lock value into a publicized script that we'd then
have to spend BACK out — pointless. Ref-script attachment is only
on the recipient (`to`) output.

This unblocks Track B-fast step 3 of the preprod DAO bringup —
deploying the 11 Agora script bytecodes (governor / stakes /
proposal / treasury / mutate / noOp / treasuryWithdrawal validators
+ GST / StakeST / ProposalST / GAT minting policies) as reference
UTxOs against Sulkta's preprod wallet.

No new tests in this commit — Phase 2 (Plutus-policy mint with
custom output) lands in a follow-up that will exercise this path
end-to-end against a real chain submit on preprod.

crates/aldabra-core/src/lib.rs

@@ -69,10 +69,12 @@ pub use governance::{
     DRepTarget, VoteChoice, DREP_REGISTRATION_DEPOSIT_LOVELACE,
 };
 pub use tx::{
-    build_signed_payment, build_signed_payment_with_assets, build_unsigned_payment,
-    build_unsigned_payment_with_assets, hex_decode, AssetSpec, InputUtxo, PaymentSummary,
-    ProtocolParams, UnsignedPayment,
+    build_signed_payment, build_signed_payment_extras, build_signed_payment_with_assets,
+    build_unsigned_payment, build_unsigned_payment_extras, build_unsigned_payment_with_assets,
+    hex_decode, AssetSpec, InputUtxo, PaymentSummary, ProtocolParams, ReferenceScriptSpec,
+    UnsignedPayment,
 };
+pub use pallas_txbuilder::ScriptKind;
 
 #[derive(Debug, Error)]
 pub enum WalletError {