videre-host: test that a venue call with no registry service returns UnknownVenue

[mfw78]

From review of #443 (comment). Confirmed still valid at HEAD. Target: L2 videre-host.

Supervisor::boot_single builds services via HostServices::from_extensions alone and never seeds the venue-registry service. A manifest importing videre:venue/client under that path hits the service-missing case: services.get::<VenueRegistry>(VenueRegistry::NAMESPACE) returns None at client.rs:24, so every quote/submit returns VenueError::UnknownVenue. Real and intentional, but unpinned.

The existing UnknownVenue tests cover a different path — the adapter-map miss, where the registry service is present and the venue id just is not installed (unknown_venue_is_rejected_without_touching_an_adapter, and the platform.rs "unlisted venue id" assertion, both landing on registry.rs:374). Neither drives the service-lookup miss at client.rs:24.

Change

Add a boot_single-based test that boots a module importing videre:venue/client with no registry service registered, and asserts quote/submit return UnknownVenue.

Acceptance criteria

• A test exercises the services.get::<VenueRegistry> = None branch end to end and asserts UnknownVenue.

[mfw78]

Landed via #531 (squash-merged into dev/m1 as ee7848e). Closing manually since the merge target is not the default branch.