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/ai_serving/planner/specialized/files/decision.rs

@@ -109,6 +109,7 @@ pub(super) async fn maybe_build_local_gemini_files_decision_payload_for_candidat
         client_session_affinity: input.client_session_affinity.as_ref(),
         routing_policy: input.routing_policy.as_ref(),
         scheduler_affinity_epoch: eligible.orchestration.scheduler_affinity_epoch,
+        sticky_key_attempts: eligible.orchestration.sticky_key_attempts,
         client_requested_stream: spec_metadata.require_streaming,
         upstream_is_stream: spec_metadata.require_streaming,
         has_envelope: false,

apps/aether-gateway/src/ai_serving/planner/specialized/image/decision.rs

@@ -122,6 +122,7 @@ pub(super) async fn maybe_build_local_openai_image_decision_payload_for_candidat
             client_session_affinity: input.client_session_affinity.as_ref(),
             routing_policy: input.routing_policy.as_ref(),
             scheduler_affinity_epoch: eligible.orchestration.scheduler_affinity_epoch,
+            sticky_key_attempts: eligible.orchestration.sticky_key_attempts,
             client_requested_stream: spec_metadata.require_streaming,
             upstream_is_stream,
             has_envelope: false,

apps/aether-gateway/src/ai_serving/planner/specialized/video/decision.rs

@@ -90,6 +90,7 @@ pub(super) async fn maybe_build_local_video_create_decision_payload_for_candidat
         client_session_affinity: input.client_session_affinity.as_ref(),
         routing_policy: input.routing_policy.as_ref(),
         scheduler_affinity_epoch: eligible.orchestration.scheduler_affinity_epoch,
+        sticky_key_attempts: eligible.orchestration.sticky_key_attempts,
         client_requested_stream: false,
         upstream_is_stream: false,
         has_envelope: false,