Fix stale observatory status after outbound removal

[Alaxay8]

Summary

Prune stale observatory statuses when an outbound is no longer returned by the handler selector.

Problem

observatory.Observer.updateStatus() didn't remove entries for outbounds that had already been removed. As a result, GetObservation() could keep returning stale OutboundStatus items after outbound removal.

Changes

• prune statuses whose outbound tags are no longer active
• add tests covering removed outbound pruning
• preserve status fields for remaining active outbounds
• clear all statuses when no active outbounds remain

Validation

• go test ./app/observatory ./app/observatory/burst
• manual runtime check with HandlerService and ObservatoryService
• removed an outbound via API
• confirmed the removed tag no longer appears in GetOutboundStatus