fix(performance): retire GPUs that stop reporting (#1969)

* fix(performance): retire GPUs that stop reporting

Track consecutive sample absence so transient misses render unavailable data without immediately removing the adapter. Retire the live adapter after three visible misses while preserving the selected ID for reconnection.

* fix(performance): align GPU fallback surfaces

Skip adapters whose latest sample is missing when resolving the fallback GPU. Make the classic dashboard consume the shared effective selection while preserving the stored user intent for reconnection.