* vector: DeleteIndex format guard, sticky discovery, advertise normalize
- handleDeleteIndex verifies the table carries the Lance format before
DeleteTable — an Iceberg table under the same namespace is not an
index and must not be removed by it.
- discovery keeps the current worker while it is still registered —
membership-order churn can no longer cancel in-flight calls, and the
resolver closes each master conn inside a 5s deadline.
- advertised_addr strips scheme and .grpcPort so the UDP probe reaches
every supported master form.
* vector: empty-follower retry, format check without read grant
- discoverVectorWorkers keeps looking past an empty master reply —
followers list nothing when workers registered with the leader.
- the DeleteIndex format check uses the internal catalog read, so
DeleteTable-only callers don't gain a GetTable requirement, and the
format must be Lance exactly — format-less tables no longer pass.