Conjoined EF Core contexts advertise TenancyStyle "Single" in DbContextUsage descriptors — CritterWatch gating gap

[jeremydmiller]

Residual from the conjoined EF Core multi-tenancy epic (#3465), Phase 3 (#3464). The #3464 design promised:

Descriptors: extend TenantedDbContextUsageSource<T> / DbContextUsage so a conjoined context advertises DatabaseCardinality.DynamicMultiple plus tenant ids on its single DatabaseDescriptor, giving CritterWatch what it needs to show the Tenants tab with actions.

That bullet did not land in #3498. As shipped (6.21.0 / 6.22.0-alpha.1):

• The tenancy-style discriminator in src/Persistence/Wolverine.EntityFrameworkCore/Internals/DbContextUsageSource.cs switches on the IDbContextBuilder<T> implementation type name and only knows TenantedDbContextBuilderByDbDataSource / TenantedDbContextBuilderByConnectionString; ConjoinedDbContextBuilder<T> falls through to "Single".
• ConjoinedDbContextBuilder<T>.Cardinality returns DatabaseCardinality.Single and FindAllAsync() returns only the main context, so the descriptor carries no tenant ids.
• No test in EfCoreTests.MultiTenancy/ConjoinedTenancy/ asserts the DbContextUsage shape for a conjoined registration.

So a conjoined app looks exactly like a plain single-DB app to CritterWatch's descriptor-driven UI. Tenant management still lights up (the IDynamicTenantSource<string> registration shipped and is what the satellite handlers fan out over), but the UI gating/badging side (JasperFx/CritterWatch#720) has nothing to distinguish conjoined from single.

Acceptance criteria

• A conjoined registration's DbContextUsage is distinguishable from a plain single-DB one (a "Conjoined" tenancy style and/or the promised DynamicMultiple cardinality — settle the exact shape with the CritterWatch#720 consumer, since conjoined is one physical database with a dynamic tenant list, which neither existing cardinality models cleanly).
• Tenant ids from the wolverine_tenants registry are surfaced on the descriptor (masked connection info as today).
• Compliance-battery coverage in EfCoreTests.MultiTenancy/ConjoinedTenancy/ asserting the descriptor shape.

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