feat!: genesis-pinned operator set, server identity with an encrypted control link, key-less join codes; release key continuity

Join codes need no passkey touch and carry only public values (genesis
fingerprint, owner credentials, installer hashes). Nodes pin the genesis and
owners at enrollment and only follow passkey-signed operator set versions.
The panel's server key is listed in the set; pinned nodes require its
signature and run the control link under AES-256-GCM. Password sessions carry
no capabilities. The updater adopts a next_key from a signed manifest.

Bump version to 0.2.0. [CI SKIP]

backend/fleet/tools/fleet-enroll/Program.cs

@@ -12,7 +12,7 @@ string? name = Arg("--name");
 string? directory = Arg("--identity-dir");
 if (server is null || join is null || name is null || directory is null)
 {
-    Console.Error.WriteLine("usage: fleet-enroll --server <url> --join <token> --name <node name> --identity-dir <dir> [--meta <json>] [--version <v>] [--role agent|probe --seed <code seed> --genesis <operator fingerprint>]");
+    Console.Error.WriteLine("usage: fleet-enroll --server <url> --join <token> --name <node name> --identity-dir <dir> [--meta <json>] [--version <v>] [--genesis <trust root fingerprint> --controllers <passkey credential ids, comma separated>]");
     return 2;
 }
 
@@ -30,13 +30,12 @@ if (Arg("--meta") is { } metaText)
     }
 }
 
-string? seed = Arg("--seed");
 string? genesis = Arg("--genesis");
-string role = Arg("--role") ?? "agent";
+string[] controllers = (Arg("--controllers") ?? "").Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
 
 using var http = new HttpClient { Timeout = TimeSpan.FromSeconds(30) };
 Result<EnrollmentResult> result = await EnrollmentClient.EnrollAsync(
-    http, new Uri(server), join, name, directory, Arg("--version") ?? "0.0.0", meta, TimeProvider.System, CancellationToken.None, seed, genesis, role);
+    http, new Uri(server), join, name, directory, Arg("--version") ?? "0.0.0", meta, TimeProvider.System, CancellationToken.None, genesis, controllers);
 if (!result.TryGet(out EnrollmentResult? enrolled, out FleetError? error))
 {
     Console.Error.WriteLine($"enrollment failed ({error.Code}): {error.Message}");