feat(escrow_wip): EscrowDatum / EscrowRedeemer / EscrowValue codecs

⚠ WIP — UNAUDITED. Feature-gated behind `escrow_wip`; out of default builds.

Mirrors aiken validator at aiken-escrow/escrow/validators/escrow.ak (also
WIP). Spec at aiken-escrow/README.md.

Five-redeemer two-party agreement-with-veto escrow:
- Open → both sign Agree → Agreed{at} → Settle (after lock_period)
- Agreed → either party Veto → per-contributor refund
- Open → Refund (after open_deadline) → per-contributor refund

Datum: ProductIsData (Constr 0 [a, b, recipient, deadline, lock, state, deposits]).
EscrowState: enum Open | Agreed{at} encoded as Constr 0/1 (with payload).
EscrowDeposit: per-contributor (pkh, Value) entry, Constr 0.
EscrowValue: Plutus Map<PolicyId, Map<AssetName, Int>>; preserves on-chain
ordering for cbor-equality checks the validator does on continuing-output
deposits diff.

Tests: 10 codec roundtrips (Open/Agreed states, ada-only/multi-asset values,
deposit lookup by pkh, value-merge sum). All pass under
`cargo test -p aldabra-dao --features escrow_wip escrow::`.

Builders + MCP tools land in follow-up commits on this branch.

crates/aldabra-dao/Cargo.toml

@@ -71,6 +71,13 @@ thiserror = { workspace = true }
 # Logging.
 tracing = { workspace = true }
 
+[features]
+default = []
+# WIP / unaudited two-party escrow validator + builders + types. Compiled
+# out of default builds until external audit lands. Enable with
+# --features escrow_wip from the workspace root.
+escrow_wip = []
+
 [dev-dependencies]
 # DaoStore tests use a temp dir as the data root.
 tempfile = "3"