feat(sentinel): make sentinel mandatory on regular servers

Remove the enable/disable toggle from the server UI, logs page, and
Sentinel API so is_sentinel_enabled is derived and read-only. Enable
existing regular servers via migration, start Sentinel after validate-
and-install, and drop the daily ServerManagerJob restart.

app/Jobs/ValidateAndInstallServerJob.php

@@ -202,6 +202,9 @@ class ValidateAndInstallServerJob implements ShouldBeEncrypted, ShouldQueue
             // Broadcast events to update UI
             ServerValidated::dispatch($this->server->team_id, $this->server->uuid);
             ServerReachabilityChanged::dispatch($this->server);
+            if ($this->server->isSentinelEnabled()) {
+                CheckAndStartSentinelJob::dispatch($this->server);
+            }
 
         } catch (\Throwable $e) {
             Log::error('ValidateAndInstallServer: Exception occurred', [