feat(simnet): add SimNet protocol end-to-end support

- model: SimNet protocol fields + NormalizeSimnet; type+port protocol uniqueness
- server config: OmnXT runtime config delivery via compatible() simnet case
- credentials: derive per-user psk/key_id from subscription (pkg/simnet), no new table
- subscription: adapter buildOmnxtSimnetConfigs + base64 buildOmnxtProtocolLinks + OmnXT SimNet application (migration 02161)
- UA gating: hide experimental protocols from non first-party clients (download + JSON node-list)
- admin: normalize simnet on create/update and on GET responses
- tests: 21 simnet unit tests; full suite green

internal/logic/admin/server/updateServerLogic.go

@@ -100,6 +100,8 @@ func (l *UpdateServerLogic) UpdateServer(req *types.UpdateServerRequest) error {
 				}
 			}
 		}
+		// Simnet: apply defaults / normalize (no-op for other protocols)
+		protocol.NormalizeSimnet()
 		protocols = append(protocols, protocol)
 	}
 	err = data.MarshalProtocols(protocols)