Expose Arena ELO sync in feature flags (#3821)

Adds ARENA_ELO_SYNC_ENABLED to the Dashboard Feature Flags registry (DB-overridable),
routes Arena ELO startup/status checks through the shared feature-flag resolver while
preserving the existing env fallback, and refreshes env docs (adds the missing
STREAM_READINESS_TIMEOUT_MS example) so env/doc sync stays green.

Integrated into release/v3.8.25.

Co-authored-by: R.D. <rogerproself@gmail.com>

src/shared/constants/featureFlagDefinitions.ts

@@ -199,7 +199,7 @@ export const FEATURE_FLAG_DEFINITIONS: FeatureFlagDefinition[] = [
     warningLevel: "info",
   },
 
-  // ──────────────── Runtime (9) ────────────────
+  // ──────────────── Runtime (10) ────────────────
   {
     key: "OMNIROUTE_MCP_ENFORCE_SCOPES",
     label: "MCP Enforce Scopes",
@@ -302,6 +302,17 @@ export const FEATURE_FLAG_DEFINITIONS: FeatureFlagDefinition[] = [
     requiresRestart: false,
     warningLevel: "info",
   },
+  {
+    key: "ARENA_ELO_SYNC_ENABLED",
+    label: "Arena ELO Sync",
+    description: "Enable periodic Arena AI leaderboard ELO sync for model intelligence rankings.",
+    descriptionI18nKey: "featureFlagArenaEloSyncEnabledDescription",
+    category: "runtime",
+    defaultValue: "true",
+    type: "boolean",
+    requiresRestart: false,
+    warningLevel: "info",
+  },
 
   // ──────────────── CLI (3) ────────────────
   {

src/shared/utils/featureFlags.ts

@@ -75,3 +75,7 @@ export function isCcCompatibleProviderEnabled(): boolean {
 export function isModelCatalogNamesEnabled(): boolean {
   return isFeatureFlagEnabled("MODEL_CATALOG_INCLUDE_NAMES");
 }
+
+export function isArenaEloSyncEnabled(): boolean {
+  return isFeatureFlagEnabled("ARENA_ELO_SYNC_ENABLED");
+}