Improve failover controls and preserve manual switching state

.tmp-tests/harbor-startup-recovery-xqwmBz/subscription-cache.json

@@ -0,0 +1 @@
+{"url":"https://cache.example/subscription-b","config":{"outbounds":[{"id":"server-b","label":"Cache server","host":"cache.example","port":8443,"protocol":"vless","type":"vless","tag":"Cache server","server":"cache.example","server_port":8443}]},"servers":[{"id":"server-b","label":"Cache server","host":"cache.example","port":8443,"protocol":"vless","type":"vless","tag":"Cache server","server":"cache.example","server_port":8443}]}