refactor: remove proxy admin endpoint (#13687)

## Summary
- delete the network proxy admin server and its runtime listener/task
plumbing
- remove the admin endpoint config, runtime, requirement, protocol,
schema, and debug-surface fields
- update proxy docs to reflect the remaining HTTP and SOCKS listeners
only

codex-rs/network-proxy/src/runtime.rs

@@ -1251,42 +1251,6 @@ mod tests {
         assert!(validate_policy_against_constraints(&config, &constraints).is_err());
     }
 
-    #[test]
-    fn validate_policy_against_constraints_disallows_non_loopback_admin_without_managed_opt_in() {
-        let constraints = NetworkProxyConstraints {
-            dangerously_allow_non_loopback_admin: Some(false),
-            ..NetworkProxyConstraints::default()
-        };
-
-        let config = NetworkProxyConfig {
-            network: NetworkProxySettings {
-                enabled: true,
-                dangerously_allow_non_loopback_admin: true,
-                ..NetworkProxySettings::default()
-            },
-        };
-
-        assert!(validate_policy_against_constraints(&config, &constraints).is_err());
-    }
-
-    #[test]
-    fn validate_policy_against_constraints_allows_non_loopback_admin_with_managed_opt_in() {
-        let constraints = NetworkProxyConstraints {
-            dangerously_allow_non_loopback_admin: Some(true),
-            ..NetworkProxyConstraints::default()
-        };
-
-        let config = NetworkProxyConfig {
-            network: NetworkProxySettings {
-                enabled: true,
-                dangerously_allow_non_loopback_admin: true,
-                ..NetworkProxySettings::default()
-            },
-        };
-
-        assert!(validate_policy_against_constraints(&config, &constraints).is_ok());
-    }
-
     #[test]
     fn validate_policy_against_constraints_disallows_allow_all_unix_sockets_without_managed_opt_in()
     {