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/passthrough/provider/family/payload.rs

@@ -203,6 +203,7 @@ pub(crate) async fn maybe_build_local_same_format_provider_decision_payload_for_
                 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: body_json
                     .get("stream")
                     .and_then(serde_json::Value::as_bool)