feat(dao-config): Phase 4 prerequisite fields + ScriptRefs

DaoConfig gains optional fields for Phase 4 (proposal_create) work:
- proposal_addr        — proposal validator address (bech32)
- stake_st_policy      — StakeST minting policy id (56 hex)
- proposal_st_policy   — ProposalST minting policy id (56 hex)
- script_refs          — cached reference UTxO refs for each Agora script
                         (governor / stake / proposal / treasury validators
                         + stake_st / proposal_st minting policies)

All fields optional with serde defaults so existing configs keep loading.
Will be populated by upcoming `dao_discover_scripts` MCP tool that audits
on-chain state under a known governor_addr.

Test fixture also corrected: stakes_addr now uses Sulkta's real per-DAO
parameterized stake-validator address (`addr1w8msu7p...`) instead of the
shared MLabs deployer (`addr1w9gexmeunzsy...`) — matches audit findings.

aldabra-mcp dao_register tool initializes new optionals to None so
DaoConfig construction stays explicit.

crates/aldabra-mcp/src/tools.rs

@@ -30,7 +30,7 @@ use std::sync::Arc;
 
 use aldabra_chain::{ChainBackend, KoiosClient};
 use aldabra_dao::agora::stake::Credential as DaoCredential;
-use aldabra_dao::config::{DaoConfig, DaoNetwork, DaoStore};
+use aldabra_dao::config::{DaoConfig, DaoNetwork, DaoStore, ScriptRefs};
 use aldabra_dao::reader::{DaoReader, KoiosDaoReader};
 use aldabra_core::plutus_cost_models::PLUTUS_V3_COST_MODEL_PREPROD;
 use aldabra_core::{
@@ -1340,6 +1340,12 @@ impl WalletService {
                 Some("preview") => DaoNetwork::Preview,
                 _ => DaoNetwork::Mainnet,
             },
+            // Optional discovery fields — populated by `dao_discover_scripts`
+            // after registration.
+            proposal_addr: None,
+            stake_st_policy: None,
+            proposal_st_policy: None,
+            script_refs: ScriptRefs::default(),
         };
         self.inner
             .dao_store