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/probe/tests/Monitor.Probe.Tests/ProbeTests.cs

@@ -30,23 +30,22 @@ public sealed class ProbeTests
         return path;
     }
 
-    private static ProbeAgentsResult List(long version, params string[] ids) => new()
+    private static ProbeAgentList List(long version, params string[] ids) => new()
     {
         Version = version,
         Agents = [.. ids.Select(id => new AgentEndpoint { AgentId = new NodeId(id), Host = id + ".example", TcpPort = 7443, Spki = "c3BraQ==" })],
     };
 
     [Fact]
-    public void AgentDirectory_StartsFromBootstrap_IgnoresStaleLists_PersistsChanges_AndReloadsThem()
+    public void AgentDirectory_StartsEmpty_IgnoresStaleLists_PersistsChanges_AndReloadsThem()
     {
         string directory = NewDirectory();
         try
         {
-            var file = new ProbeFile { ProbeId = "prb_x", Bootstrap = [new BootstrapAgent { AgentId = "agt_boot", Host = "boot.example", TcpPort = 7443, Spki = "c3BraQ==" }] };
-            var directoryA = new AgentDirectory(new ConfigStore(directory), directory, file, NullNodeLog.Instance);
+            var directoryA = new AgentDirectory(new ConfigStore(directory), directory, NullNodeLog.Instance);
             int changes = 0;
             directoryA.Changed += () => changes++;
-            Assert.Equal(["agt_boot"], directoryA.Agents.Select(a => a.AgentId));
+            Assert.Empty(directoryA.Agents);
 
             directoryA.Apply(List(5, "agt_1", "agt_2"));
             Assert.Equal(1, changes);
@@ -57,8 +56,8 @@ public sealed class ProbeTests
             Assert.Equal(1, changes);
             Assert.Equal(5, directoryA.Version);
 
-            // The next start uses the saved list, not the bootstrap one
-            var directoryB = new AgentDirectory(new ConfigStore(directory), directory, file, NullNodeLog.Instance);
+            // The next start uses the saved list while the panel is not reachable yet
+            var directoryB = new AgentDirectory(new ConfigStore(directory), directory, NullNodeLog.Instance);
             Assert.Equal(["agt_1", "agt_2"], directoryB.Agents.Select(a => a.AgentId));
             Assert.Equal(5, directoryB.Version);
         }
@@ -69,15 +68,14 @@ public sealed class ProbeTests
     }
 
     [Fact]
-    public void AgentDirectory_FallsBackToBootstrap_WhenTheSavedFileIsCorrupt()
+    public void AgentDirectory_StartsEmpty_WhenTheSavedFileIsCorrupt()
     {
         string directory = NewDirectory();
         try
         {
             new ConfigStore(directory).Write(AgentDirectory.FileName, "{ not json"u8.ToArray());
-            var file = new ProbeFile { Bootstrap = [new BootstrapAgent { AgentId = "agt_boot", Host = "h", TcpPort = 1, Spki = "AA==" }] };
-            var loaded = new AgentDirectory(new ConfigStore(directory), directory, file, NullNodeLog.Instance);
-            Assert.Equal(["agt_boot"], loaded.Agents.Select(a => a.AgentId));
+            var loaded = new AgentDirectory(new ConfigStore(directory), directory, NullNodeLog.Instance);
+            Assert.Empty(loaded.Agents);
         }
         finally
         {