feat(dao): scaffold aldabra-dao crate (Phase 1 reads)

Adds a 4th workspace crate `aldabra-dao` for native Agora-on-Cardano
DAO interaction. Multi-DAO from day one — DaoConfig per DAO at
\$ALDABRA_DATA/daos/<name>.json + .active selector. Sulkta DAO and any
community Agora deployment (Bob's DAO, Alice's DAO) are first-class.

Phase 0 type port complete:
- StakeDatum, StakeRedeemer, ProposalAction, ProposalLock, Credential
- ProposalDatum, ProposalRedeemer, ProposalStatus, ProposalThresholds,
  ProposalTimingConfig, ProposalVotes
- GovernorDatum, GovernorRedeemer
- All Constr indices verified against Agora source makeIsDataIndexed
  + EnumIsData declarations (Stake/Proposal/Governor/Action/Status all
  cross-referenced)
- Round-trip tests for every type

Phase 1 read surface (this commit):
- DaoStore: DaoConfig load/save/list/remove + active-DAO selector with
  first-register-becomes-active UX. 8 unit tests.
- DaoReader trait + KoiosDaoReader impl for get_governor + list_stakes.
  list_proposals stubbed pending Phase 4 proposal-script-address discovery.
- Stake address sharing handled: list_stakes filters on gov_token_policy
  (the shared MLabs stakes addr serves many DAOs).

Stubs for upcoming phases:
- agora/treasury.rs (Phase 4 — treasury spend helpers)
- agora/authority_token.rs (Phase 4 — GAT mint/burn)
- agora/reference_scripts.rs (Phase 2/3 — independent script-hash discovery
  per Sulkta's choice 2026-05-05; computed locally, never trust MLabs registry)
- builder/mod.rs (per-operation Plutus tx builders, populated phase-by-phase)

Spec doc + decisions: internal notes in workspace.

Effects map (`ProposalDatum.effects`) kept as raw PlutusData for round-trip
integrity until Phase 4 (proposal create) needs typed access.

ExUnits strategy locked: Koios tx_evaluate from day one (no hardcoded values).
Wired up in Phase 2 alongside reference-script discovery.

Cargo.toml

@@ -1,16 +1,17 @@
 # Cargo workspace root for aldabra.
 #
-# Three crates:
+# Four crates:
 #   aldabra-core   — key derivation, signing, types, mnemonic handling
 #   aldabra-chain  — pluggable chain backends (Koios, Ogmios). Trait-first.
-#   aldabra-mcp    — binary; the MCP server, glues core+chain together.
+#   aldabra-dao    — Agora-on-Cardano DAO interaction; multi-DAO from day 1.
+#   aldabra-mcp    — binary; the MCP server, glues core+chain+dao together.
 #
 # Named for the Aldabra giant tortoise (Aldabrachelys gigantea) — endemic
 # to the Aldabra atoll in the Seychelles, up to 250 kg, 150-year lifespan.
 # Long-lived, defended, slow but unstoppable. Fitting metaphor for a
 # wallet that holds your money.
 #
-# Workspace deps are pinned here so all three crates use the same versions.
+# Workspace deps are pinned here so all crates use the same versions.
 # Add a dep here, then reference it in each crate's Cargo.toml as
 #   foo = { workspace = true }
 [workspace]
@@ -18,6 +19,7 @@ resolver = "2"
 members = [
     "crates/aldabra-core",
     "crates/aldabra-chain",
+    "crates/aldabra-dao",
     "crates/aldabra-mcp",
 ]