feat(escrow): drop escrow_wip feature gate, ship as default surface

Per Sulkta 2026-05-09 directive: after the audit + preprod E2E green-light
(6/6 builders, 9 successful txs, 0 failures), drop the compile-time gate
and integrate escrow as a default-on feature. The "not third-party
audited" framing becomes a runtime notice carried by escrow_open_unsigned
rather than a Cargo feature.

Changes:
- aldabra-dao/Cargo.toml: drop [features] block + escrow_wip = []
- aldabra-dao/src/agora/mod.rs: pub mod escrow (no cfg gate)
- aldabra-dao/src/builder/mod.rs: 6 escrow_* modules unconditional
- aldabra-mcp/Cargo.toml: drop features = ["escrow_wip"] from dao dep
- aldabra-mcp/src/tools.rs:
  - Drop "WIP — UNAUDITED:" prefix from all 6 escrow tool descriptions
  - Drop "wip_warning" JSON field from all 6 spend-tool responses
  - Add "audit_notice" field on escrow_open_unsigned response only
    (per Sulkta's framing — once-per-escrow-conversation, not repeated
    on every subsequent tool)
  - Update section header comment to reflect post-WIP status
- 7 escrow source files (1 agora + 6 builder): replace
  "WIP / UNAUDITED. Feature-gated behind escrow_wip" docstring with
  "Not third-party audited — preprod-only" + audit doc reference

Verified: 133 dao tests pass (was 132 under --features escrow_wip;
+1 from the rejects_no_initial_contributor test that's now always
compiled). aldabra-mcp release build clean.

The runtime audit_notice on escrow_open_unsigned reads:
  "This escrow validator has had an internal review and a 9-tx preprod
   E2E pass, but has NOT been audited by an external third party. Use
   at your own risk. If the user is opening this with anything beyond
   test-net or low-value funds, pass this notice along and confirm they
   accept the risk. Validator hash: a8081acef26935d9b5f44b92052178e17301b6d6e6808c91c5b56f5d."

This carries the same caveat the WIP framing did, but in a form the
calling agent can surface inline to the user opening the escrow.

crates/aldabra-mcp/Cargo.toml

@@ -20,18 +20,7 @@ path = "src/main.rs"
 [dependencies]
 aldabra-core = { path = "../aldabra-core" }
 aldabra-chain = { path = "../aldabra-chain" }
-# Always pulls aldabra-dao/escrow_wip so the MCP binary can expose
-# the escrow_* tool surface unconditionally. The "WIP — UNAUDITED:"
-# prefix in every tool's description is the runtime gate; the dao
-# crate's escrow_wip feature stays gated for downstream Rust consumers
-# that want to opt out at the source level.
-#
-# Rationale: rmcp 0.1.5's #[tool(tool_box)] macro doesn't compose with
-# #[cfg] on individual methods (it scans the impl AST and references
-# every #[tool]-tagged method's generated wrapper, regardless of cfg
-# eligibility). Force-pulling the feature at the dep level avoids the
-# macro/cfg conflict.
-aldabra-dao = { path = "../aldabra-dao", features = ["escrow_wip"] }
+aldabra-dao = { path = "../aldabra-dao" }
 
 # Used directly in tools.rs to decode the wallet's bech32 address into a
 # payment-credential hash (so `dao_my_stake` can match against StakeDatum.owner).