feat(routing): move sticky-key retries into routing policy with lazy attempts

Replace the provider/endpoint max_retries fields as the source of same-key
retries with a routing policy setting, sticky_key_attempts (default 2). Only
the first-ranked candidate is retried on the same key; every failover
candidate gets a single attempt so failover keeps advancing instead of
retrying each fallback key.

Materialize exactly one attempt per candidate and derive same-key retries in
the attempt loop after a candidate-scoped failure, so the retry budget no
longer inflates up-front materialization and needs no upper bound. The budget
travels in the report context; retries reuse the plan with a fresh candidate
id and incremented retry index. Pool groups only retry their first key within
the retry-index stride.

Expose the setting in the routing profile editor and the set_scheduling rule
action, and drop the max_retries input from the provider form.

apps/aether-gateway/src/dispatch/pool_scheduler.rs

@@ -1951,11 +1951,13 @@ fn apply_pool_orchestration(
     orchestration: PoolCandidateOrchestration,
 ) -> EligibleLocalExecutionCandidate {
     let scheduler_affinity_epoch = candidate.orchestration.scheduler_affinity_epoch;
+    let sticky_key_attempts = candidate.orchestration.sticky_key_attempts;
     candidate.orchestration = LocalExecutionCandidateMetadata {
         candidate_group_id: orchestration.candidate_group_id,
         pool_key_index: orchestration.pool_key_index,
         pool_key_lease: None,
         scheduler_affinity_epoch,
+        sticky_key_attempts,
     };
     candidate
 }
@@ -2159,6 +2161,7 @@ mod tests {
                 pool_key_index: Some(0),
                 pool_key_lease: None,
                 scheduler_affinity_epoch: None,
+                sticky_key_attempts: None,
             }
         );
         assert_eq!(reordered[1].orchestration.pool_key_index, Some(1));
@@ -2176,6 +2179,7 @@ mod tests {
                 pool_key_index: None,
                 pool_key_lease: None,
                 scheduler_affinity_epoch: None,
+                sticky_key_attempts: None,
             }
         );
     }
@@ -5072,6 +5076,7 @@ mod tests {
             priority_mode: RoutingSetPriorityMode::Provider,
             scheduling_mode: RoutingSchedulingMode::CacheAffinity,
             keep_priority_on_conversion: false,
+            sticky_key_attempts: aether_routing_core::DEFAULT_STICKY_KEY_ATTEMPTS,
             ranking_overlay: RankingOverlay {
                 allowed_keys: key_ids.into_iter().map(str::to_string).collect(),
                 ..RankingOverlay::default()

apps/aether-gateway/src/dispatch/refs.rs

@@ -208,6 +208,7 @@ mod tests {
                 pool_key_index: None,
                 pool_key_lease: None,
                 scheduler_affinity_epoch: None,
+                sticky_key_attempts: None,
             },
             ranking: None,
         }