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/src/Fleet.Server.Link/NodeConnection.Wire.cs

@@ -30,6 +30,19 @@ internal sealed partial class NodeConnection
 
             if (result.EndOfMessage)
             {
+                if (_cipher is { } cipher)
+                {
+                    // 加密链路上只接受通过认证的二进制帧；明文、被改过的、重放的、乱序的一律断开
+                    if (result.MessageType != WebSocketMessageType.Binary || !cipher.TryOpen(writer.WrittenSpan, out byte kind, out byte[] plain))
+                    {
+                        _closeReason ??= "frame failed authentication";
+                        await _socket.CloseOutputAsync(WebSocketCloseStatus.PolicyViolation, "frame failed authentication", CancellationToken.None);
+                        return null;
+                    }
+
+                    return new Frame(kind == 0, plain);
+                }
+
                 return new Frame(result.MessageType == WebSocketMessageType.Text, writer.WrittenSpan.ToArray());
             }
         }