feat: global failover + dashboard model config section

- Failover is now global (account-level, not per-channel)
- Dashboard shows role model config (Owner/Reviewer/Arbiter + MoA refs)
- Dashboard shows failover status when active
- Auto-clear failover on successful Claude rotation
- Remove per-channel lease writes from failover path

src/config.ts

@@ -191,8 +191,7 @@ function parseMoaReferenceModels(): MoaModelConfig[] {
 export function getMoaConfig(): MoaConfig {
   const referenceModels = parseMoaReferenceModels();
   return {
-    enabled:
-      getEnv('MOA_ENABLED') === 'true' && referenceModels.length > 0,
+    enabled: getEnv('MOA_ENABLED') === 'true' && referenceModels.length > 0,
     referenceModels,
   };
 }