Cardano Updates

Replace mkUnsignedTx + mkByronWitness/mkShelleyWitness with
mkLedgerTx + mkByronWitnessLedger/mkShelleyWitnessLedger in
the duplicated test module.

All 8 golden hex string tests pass — ledger-native construction
produces byte-identical CBOR to the cardano-api construction.

Alternative to Transaction.hs that builds transactions using
mkLedgerTx (ledger lenses) instead of Cardano.Api.TxBodyContent.

Implements mkTransactionLedger and constructUnsignedTxLedger with
key-witnessed withdrawals and certificates. Minting, script
witnesses, and reference scripts are TODO.

Remaining cardano-api dependencies (with TODOs):
- signTransaction takes Cardano.NetworkId
- sealWriteTx roundtrips through cardano-api
- certificateFromDelegationAction returns Cardano.Certificate

Replace InAnyCardanoEra Cardano.Tx with EraValue Read.Tx as the
decoded transaction field. The CBOR bytes remain the canonical
representation.

Temporary cardano-api reconstruction functions kept for callers
that haven't migrated yet (cardanoTxIdeallyNoLaterThan,
getSealedTxBody, getSealedTxWitnesses). These deserialize from
bytes on demand.

fromSealedTx in Sealed.hs becomes trivial: just reads the field.

Replace mkUnsignedTx + mkByronWitness/mkShelleyWitness with
mkLedgerTx + mkByronWitnessLedger/mkShelleyWitnessLedger in
the duplicated test module.

All 8 golden hex string tests pass — ledger-native construction
produces byte-identical CBOR to the cardano-api construction.

Alternative to Transaction.hs that builds transactions using
mkLedgerTx (ledger lenses) instead of Cardano.Api.TxBodyContent.

Implements mkTransactionLedger and constructUnsignedTxLedger with
key-witnessed withdrawals and certificates. Minting, script
witnesses, and reference scripts are TODO.

Remaining cardano-api dependencies (with TODOs):
- signTransaction takes Cardano.NetworkId
- sealWriteTx roundtrips through cardano-api
- certificateFromDelegationAction returns Cardano.Certificate

The pinned cardano-balance-transaction (98e7f41) still depends on
cardano-api. Add US1 as a gate: pin the cardano-api-free version
first. Document the breaking API changes (CardanoApiEra removal,
toCardanoApiTx/fromCardanoApiTx removal) that cascade into wallet
transaction, delegation, and voting code.

Additive-then-remove strategy: add ledger-native paths alongside
cardano-api, migrate consumers one module at a time (each commit
compiles), then atomically remove cardano-api in a single commit.

51 tasks across 5 phases (A-E). Covers pin bump, new type paths,
consumer migration, atomic removal, and verification.

Replace InAnyCardanoEra Cardano.Tx with EraValue Read.Tx as the
decoded transaction field. The CBOR bytes remain the canonical
representation.

Temporary cardano-api reconstruction functions kept for callers
that haven't migrated yet (cardanoTxIdeallyNoLaterThan,
getSealedTxBody, getSealedTxWitnesses). These deserialize from
bytes on demand.

fromSealedTx in Sealed.hs becomes trivial: just reads the field.

Rewrite spec starting from current master state where
cardano-balance-transaction and cardano-coin-selection are already
extracted. Focus on the remaining 71 imports across 45 files.
Added context section, test generator migration story (US5),
Byron support requirement (FR-013).

Spec covers the full removal across 6 phases: ledger re-exports,
TxMetadata, NetworkId, certificates, SealedTx, and tx submission.