feat(routing): make routing profiles the sole scheduler policy source

Bootstrap an enabled system-default routing group from the legacy
scheduler config keys on startup, resolve the default ordering config
from that group before falling back to the legacy keys, and stop merging
keep_priority_on_conversion with the legacy flag when a policy is
resolved. Thread the policy-derived ordering config into candidate
preselection so it no longer reads system config independently.

Add per-API-format key priority overrides so a key serving several
formats keeps independent ordering, matching the legacy
global_priority_by_format semantics. Expose keep_priority_on_conversion
in the routing profile editor and read the effective policy in the
model routing preview, monitoring metrics and provider page badge.

crates/aether-routing-core/src/actions.rs

@@ -81,6 +81,10 @@ pub enum RoutingAction {
     SetKeyPriority {
         key_id: String,
         priority: i32,
+        /// When set, the override only applies to candidates served through
+        /// this API format; otherwise it applies to the key on every format.
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        api_format: Option<String>,
     },
     JsonPatchBody {
         patch: Vec<RoutingJsonPatchOperation>,