Add explicit "no protection device" state for circuits

Circuits can now record that they deliberately have no protection device
(type NONE, shown as "–"), separate from circuits whose protection is
still open. Migration 0017 makes rated_current_a nullable.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/frontend/utils/circuit-protection-editing.ts

@@ -3,14 +3,26 @@ import type {
 } from "../../domain/models/circuit-protection-project-command.model";
 import { createDefaultCircuitProtection } from "../../domain/services/protection-device-defaults";
 import type { CircuitGroupCategory } from "../../shared/constants/circuit-group";
+import { noCircuitProtectionDeviceType } from "../../shared/constants/protection-device";
 import type {
-  CircuitTreeProtectionDeviceDto,
+  CircuitTreeCircuitProtectionDeviceDto,
 } from "../types";
 
 export function toCircuitProtectionSnapshot(
   circuitId: string,
-  protection: CircuitTreeProtectionDeviceDto
+  protection: CircuitTreeCircuitProtectionDeviceDto
 ): CircuitProtectionSnapshot {
+  if (protection.type === noCircuitProtectionDeviceType) {
+    return {
+      circuitId,
+      type: noCircuitProtectionDeviceType,
+      ratedCurrentA: null,
+      fuseUtilizationCategory: null,
+      tripCharacteristic: null,
+      rcdType: null,
+      ratedResidualCurrentMa: null,
+    };
+  }
   return {
     circuitId,
     type: protection.type,
@@ -26,8 +38,8 @@ export function toCircuitProtectionSnapshot(
 
 export function getCircuitProtectionEditorInitialValue(
   category: CircuitGroupCategory | undefined,
-  protection: CircuitTreeProtectionDeviceDto | undefined
-): CircuitTreeProtectionDeviceDto {
+  protection: CircuitTreeCircuitProtectionDeviceDto | undefined
+): CircuitTreeCircuitProtectionDeviceDto {
   if (protection) {
     return protection;
   }