fix(pool): keep schedulable keys when stale inactive scores exist

- delete pool member scores when a provider key is deactivated
- fall through to the catalog key scan when the pool score page is empty
- log skipped local candidates with a skip_reason for diagnosis
- add regressions for inactive keys with stale available scores

apps/aether-gateway/src/scheduler/candidate/resolution.rs

@@ -23,6 +23,16 @@ pub(super) fn resolve_scheduler_candidate_selectability(
         if let Some(skip_reason) =
             current_candidate_runtime_skip_reason(&candidate, runtime_snapshot, now_unix_secs)
         {
+            tracing::debug!(
+                event_name = "scheduler_candidate_skipped",
+                log_type = "event",
+                provider_id = %candidate.provider_id,
+                endpoint_id = %candidate.endpoint_id,
+                key_id = %candidate.key_id,
+                api_format = %candidate.endpoint_api_format,
+                skip_reason,
+                "scheduler candidate skipped during runtime selectability resolution"
+            );
             if emitted_skipped_keys.insert(key) {
                 skipped.push(SchedulerSkippedCandidate {
                     candidate,