Replace the CLI's Akka.NET ClusterClient transport with a simple HTTP client
targeting a new POST /management endpoint on the Central Host. The endpoint
handles Basic Auth, LDAP authentication, role resolution, and ManagementActor
dispatch in a single round-trip — eliminating the CLI's Akka, LDAP, and
Security dependencies.
Also fixes DCL ReSubscribeAll losing subscriptions on repeated reconnect by
deriving the tag list from _subscriptionsByInstance instead of _subscriptionIds.
Wired ISiteHealthCollector calls for script errors (ScriptExecutionActor),
alarm eval errors (AlarmActor), dead letters (DeadLetterMonitorActor), and
S&F buffer depth placeholder. Added instance count tracking (deployed/
enabled/disabled) to SiteHealthReport via DeploymentManagerActor. Updated
Health Dashboard UI to show instance counts per site. All metrics flow
through the existing health report pipeline via ClusterClient.
