feat!: probes link to the panel; signed release updates for container nodes [CI]

Probes connect to the panel directly and get the agent list as desired state.
CI signs the image digest of agent and probe releases, the panel forwards the
manifest, and a host updater verifies it with a local public key, pulls by
digest and rolls back when the new version is unhealthy.

backend/src/Monitor.Backend.Application/ApplicationServiceCollectionExtensions.cs

@@ -35,6 +35,7 @@ public static class ApplicationServiceCollectionExtensions
         services.AddSingleton<WindowComputer>();
         services.AddSingleton<AuthService>();
         services.AddSingleton<SettingsService>();
+        services.AddSingleton<ReleaseService>();
         services.AddSingleton<JoinTokenService>();
         services.AddSingleton<RawBrowserService>();
         services.AddSingleton<EventService>();