Honor MessageStoreRole for tenanted message stores

[outofrange-consulting]

The bug

PersistMessagesWithPostgresql(cs, "wolverine", role: MessageStoreRole.Ancillary).RegisterStaticTenants(...) produces a store that reports Main, not Ancillary.

BuildMessageStore() applies the configured Role only on the non-tenanted return path:

var settings = buildMainDatabaseSettings();   // Role = MessageStoreRole.Main, hardcoded

if (UseMasterTableTenancy)           return new MultiTenantedMessageStore(...);  // Role never applied
if (ConnectionStringTenancy != null) return new MultiTenantedMessageStore(...);  // Role never applied

settings.Role = Role;                                                            // only here
return new PostgresqlMessageStore(settings, ...);

Why it hurts

In a modular monolith where a module registers an ancillary, statically-tenanted store, the host now has two Main stores. MessageStoreCollection's constructor takes the mains.Length == 1 branch, finds two, and leaves Main as the initial NullMessageStore — no exception, no log line.

From there:

• WolverineRuntime.tryMigrateStorage() returns early on Storage is NullMessageStore, so the envelope schema is never built;
• startMessagingTransportsAsync() and the durability agent start anyway.

On PostgreSQL the app then loops forever on 42P01: relation "wolverine.wolverine_nodes" does not exist. The only workaround today is to reach for the store's DemoteToAncillary() after the fact.

The fix

Set Role in buildMainDatabaseSettings() so every return path sees it, and drop the late assignment. Role already defaults to MessageStoreRole.Main, so nothing changes for callers that don't ask for Ancillary.

The same defect is present verbatim in all five relational providers (PostgreSQL, Sql Server, Sqlite, Oracle, MySql); all are fixed here.

Tests

PostgresqlTests/message_store_role_registration.cs — three cases, no database required: ancillary single-database, ancillary with static tenants, and the Main default with static tenants. Mutation-checked: reverting the PostgreSQL fix fails the ancillary-with-tenants test and leaves the other two green.