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>

tests/protection-device.test.ts

@@ -205,6 +205,27 @@ describe("protection device defaults", () => {
     );
   });
 
+  it("maps the explicit no-protection state to a record without values", () => {
+    const none = getCircuitProtectionEditorInitialValue("single_phase", {
+      type: "NONE",
+    });
+    assert.deepEqual(none, { type: "NONE" });
+    assert.deepEqual(toCircuitProtectionSnapshot("circuit-1", none), {
+      circuitId: "circuit-1",
+      type: "NONE",
+      ratedCurrentA: null,
+      fuseUtilizationCategory: null,
+      tripCharacteristic: null,
+      rcdType: null,
+      ratedResidualCurrentMa: null,
+    });
+    // Distribution-board components never take the circuit-only state.
+    assert.equal(
+      protectionDeviceConfigurationSchema.safeParse({ type: "NONE" }).success,
+      false
+    );
+  });
+
   it("creates the agreed circuit defaults", () => {
     assert.deepEqual(createDefaultCircuitProtection("lighting"), {
       type: "LS",