fix(completion-templates): let PUT clear workOrderType with an explicit null

UpdateAsync only applied WorkOrderType when it had a value, so once a
template was restricted to one work order type no request could make it
trade-generic again. The DTO now records whether workOrderType was present
in the body: omitting it keeps the stored value, an explicit null clears
it, and a concrete value sets it. The templates page echoes the stored
legacy fields on PUT, so its behaviour is unchanged.

SeaHaven.Services/DTOs/WorkOrderDetailDTOs.cs

@@ -49,15 +49,33 @@ namespace SeaHaven.Services.DTOs
     }
 
     // Create/update body. Legacy fields are optional: on update, null leaves the
-    // stored value unchanged, as does a null Procedures list. ExtraSafetyNote is
+    // stored value unchanged, as does a null Procedures list. WorkOrderType is the
-    // always applied, so null removes the note.
+    // exception: omitting it keeps the stored value, while an explicit
+    // "workOrderType": null clears it so the template applies to every work order
+    // type of its trade. ExtraSafetyNote is always applied, so null removes the note.
     public class CompletionDocTemplateCreateDto
     {
+        private WorkOrderType? _workOrderType;
+
         public string? Name { get; set; }
         public string? ExtraSafetyNote { get; set; }
         public List<CompletionDocTemplateProcedureInputDto>? Procedures { get; set; }
         public string? ServiceKey { get; set; }
-        public WorkOrderType? WorkOrderType { get; set; }
+
+        public WorkOrderType? WorkOrderType
+        {
+            get => _workOrderType;
+            set
+            {
+                _workOrderType = value;
+                WorkOrderTypeSpecified = true;
+            }
+        }
+
+        // True when the body carried workOrderType at all, including as null.
+        [System.Text.Json.Serialization.JsonIgnore]
+        public bool WorkOrderTypeSpecified { get; private set; }
+
         public string? TemplateUrl { get; set; }
         public bool? IsActive { get; set; }
     }

SeaHaven.Services/Implementation/CompletionDocTemplateService.cs

@@ -105,7 +105,7 @@ namespace SeaHaven.Services.Implementation
             entity.ExtraSafetyNote = input.ExtraSafetyNote;
             if (input.ServiceKey != null)
                 entity.ServiceKey = input.ServiceKey;
-            if (request.WorkOrderType.HasValue)
+            if (request.WorkOrderTypeSpecified)
                 entity.WorkOrderType = request.WorkOrderType;
             if (input.TemplateUrl != null)
                 entity.TemplateUrl = input.TemplateUrl;

SeaHavenIndustries.Tests/CompletionDocTemplateServiceTests.cs

@@ -248,6 +248,42 @@ public class CompletionDocTemplateServiceTests
         Assert.Null(updated.CreatedByName);
     }
 
+    // Bodies are bound by System.Text.Json with the web defaults, as MVC does.
+    private static CompletionDocTemplateCreateDto JsonBody(string json) =>
+        System.Text.Json.JsonSerializer.Deserialize<CompletionDocTemplateCreateDto>(
+            json, new System.Text.Json.JsonSerializerOptions(System.Text.Json.JsonSerializerDefaults.Web))!;
+
+    [Fact]
+    public async Task Update_WorkOrderTypeExplicitNullClears_OmittedKeeps_ValueSets()
+    {
+        using var context = NewContext();
+        context.CompletionDocTemplates.Add(new CompletionDocTemplate
+        {
+            Id = 8,
+            Name = "HVAC PM Completion",
+            ServiceKey = "HVAC",
+            WorkOrderType = WorkOrderType.PM,
+            TemplateUrl = "",
+            IsActive = true
+        });
+        await context.SaveChangesAsync();
+        var service = NewService(context);
+
+        var omitted = JsonBody("""{"name":"HVAC Completion"}""");
+        Assert.False(omitted.WorkOrderTypeSpecified);
+        var kept = await service.UpdateAsync(Admin(), 8, omitted, CancellationToken.None);
+        Assert.Equal(WorkOrderType.PM, kept.WorkOrderType);
+
+        var cleared = await service.UpdateAsync(
+            Admin(), 8, JsonBody("""{"name":"HVAC Completion","workOrderType":null}"""), CancellationToken.None);
+        Assert.Null(cleared.WorkOrderType);
+        Assert.Null((await context.CompletionDocTemplates.AsNoTracking().SingleAsync(t => t.Id == 8)).WorkOrderType);
+
+        var set = await service.UpdateAsync(
+            Admin(), 8, JsonBody("""{"name":"HVAC Completion","workOrderType":6}"""), CancellationToken.None);
+        Assert.Equal(WorkOrderType.Reactive, set.WorkOrderType);
+    }
+
     [Fact]
     public async Task Update_MissingOrDeletedTemplate_ThrowsNotFound()
     {