phase 4.5, 4.6, 3.6 close-out: stake delegation + multisig mint primitive

stake key + reward address (4.5):
- StakeKey::stake_address(network) — bech32 (`stake1...` mainnet,
  `stake_test1...` testnet) via pallas_addresses::StakeAddress::new
  (added to the fork in the same commit since the upstream tuple
  struct had no public constructor).
- StakeKey::xprv() — crate-internal accessor for signing.
- WalletInner now holds the stake_key alongside the payment_key.
- mcp tool wallet.stake.address surfaces the bech32.

stake delegation (4.6):
- new aldabra-core::stake module:
  - parse_pool_id(bech32) → Hash<28>
  - build_signed_stake_delegation(payment, stake, network, utxos,
    change_addr, pool_bech32, register_first, params) → signed cbor.
  - if register_first: prepends a StakeRegistration cert (consumes
    a 2 ADA deposit from inputs). otherwise just delegates.
  - signs with both payment_key (body witness) and stake_key (cert
    witness). reuses sign::add_witness for both — same body-hash
    ed25519 signing path regardless of CIP-1852 chain index.
- mcp tool wallet.stake.delegate: pool_id, register_first (defaults
  true). signs + submits.

3.6 close-out — wallet.mint.unsigned mcp tool:
- exposes the existing build_unsigned_mint with caller-supplied
  PolicySpec (json), so multi-sig / treasury flows can build through
  this wallet without it auto-signing. round-trip with
  wallet.sign_partial chain → wallet.submit_signed_tx.

depends on Sulkta-Coop/pallas@feat-aux-data which gained two more
patches in the same branch:
- StakeAddress::new public constructor.
- StagingTransaction::add_certificate / clear_certificates +
  Conway::build_conway_raw decode-and-plumb for certs (filling in the
  `certificates: None, // TODO` upstream).

mcp tools: 12 → 15 (wallet.stake.address, wallet.stake.delegate,
wallet.mint.unsigned).

79 → 84 unit tests. new coverage: stake address bech32 round-trip,
pool_id bech32 parse + reject-wrong-hrp, delegation tx with + without
registration (asserts cert count, witness count, cert variants).
fork tests grew: certificates_plumb_through_to_tx_body and
no_certificates_means_none.

Cargo.lock

@@ -80,6 +80,7 @@ dependencies = [
 name = "aldabra-core"
 version = "0.0.1"
 dependencies = [
+ "bech32",
  "bip39",
  "cryptoxide",
  "ed25519-bip32",
@@ -1251,7 +1252,7 @@ checksum = "c08d65885ee38876c4f86fa503fb49d7b507c2b62552df7c70b2fce627e06381"
 [[package]]
 name = "pallas-addresses"
 version = "0.32.1"
-source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#57b36d3a7c840569d4d86f6d805a42aa4cf85347"
+source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#68221fbcb57ea499502ad23547313ff91a21ba72"
 dependencies = [
  "base58",
  "bech32",
@@ -1266,7 +1267,7 @@ dependencies = [
 [[package]]
 name = "pallas-codec"
 version = "0.32.1"
-source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#57b36d3a7c840569d4d86f6d805a42aa4cf85347"
+source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#68221fbcb57ea499502ad23547313ff91a21ba72"
 dependencies = [
  "hex",
  "minicbor",
@@ -1277,7 +1278,7 @@ dependencies = [
 [[package]]
 name = "pallas-crypto"
 version = "0.32.1"
-source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#57b36d3a7c840569d4d86f6d805a42aa4cf85347"
+source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#68221fbcb57ea499502ad23547313ff91a21ba72"
 dependencies = [
  "cryptoxide",
  "hex",
@@ -1291,7 +1292,7 @@ dependencies = [
 [[package]]
 name = "pallas-primitives"
 version = "0.32.1"
-source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#57b36d3a7c840569d4d86f6d805a42aa4cf85347"
+source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#68221fbcb57ea499502ad23547313ff91a21ba72"
 dependencies = [
  "base58",
  "bech32",
@@ -1306,7 +1307,7 @@ dependencies = [
 [[package]]
 name = "pallas-traverse"
 version = "0.32.1"
-source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#57b36d3a7c840569d4d86f6d805a42aa4cf85347"
+source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#68221fbcb57ea499502ad23547313ff91a21ba72"
 dependencies = [
  "hex",
  "itertools",
@@ -1322,7 +1323,7 @@ dependencies = [
 [[package]]
 name = "pallas-txbuilder"
 version = "0.32.1"
-source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#57b36d3a7c840569d4d86f6d805a42aa4cf85347"
+source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#68221fbcb57ea499502ad23547313ff91a21ba72"
 dependencies = [
  "hex",
  "pallas-addresses",
@@ -1339,7 +1340,7 @@ dependencies = [
 [[package]]
 name = "pallas-wallet"
 version = "0.32.1"
-source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#57b36d3a7c840569d4d86f6d805a42aa4cf85347"
+source = "git+https://git.sulkta.com/Sulkta-Coop/pallas.git?branch=feat-aux-data#68221fbcb57ea499502ad23547313ff91a21ba72"
 dependencies = [
  "bech32",
  "bip39",