fix(work-orders): name Schedule On in PastDueStatusBlocked and register SH-121 no-op

The 422 still told dispatchers to update Due Date. Point the remedy at Schedule On and make the SH-121 successor visible to EF so G6 lineage is complete.

Data.SeaHavenIndustries/Migrations/20260813193000_SH121_BoardSearchFacets.cs

@@ -1,3 +1,5 @@
+using Data.SeaHavenIndustries;
+using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Migrations;
 
 #nullable disable
@@ -10,6 +12,8 @@ namespace Data.SeaHavenIndustries.Migrations
     /// now live in <c>20260730150000_WoIsAddOn</c> (SH-184). This migration is a no-op so
     /// both PRs can land without a duplicate column.
     /// </summary>
+    [DbContext(typeof(ApplicationDbContext))]
+    [Migration("20260813193000_SH121_BoardSearchFacets")]
     public partial class SH121_BoardSearchFacets : Migration
     {
         /// <inheritdoc />

SeaHaven.Services/Implementation/WorkOrderBoardUpdateService.cs

@@ -63,7 +63,7 @@ namespace SeaHaven.Services.Implementation
 
                 var isPastDue = WorkOrderDerivedFields.IsPastDue(workOrder.ScheduledDate, workOrder.LifecycleStatus);
                 if (WorkOrderBoardMutationRules.ShouldBlockStatusChangeWhenPastDue(canonicalField, isPastDue))
-                    throw new WorkOrderBoardValidationException("PastDueStatusBlocked", "Status cannot be changed while work order is past due. Update due date first.");
+                    throw new WorkOrderBoardValidationException("PastDueStatusBlocked", "Status cannot be changed while work order is past due. Update Schedule On first.");
 
                 _mutationData.SetExpectedWorkOrderVersion(workOrder, workOrderVersion);
 

SeaHavenIndustries.Tests/WorkOrderBoardUpdateServiceTests.cs

@@ -111,6 +111,8 @@ public class WorkOrderBoardUpdateServiceTests
             }, "actor-1"));
 
         Assert.Equal("PastDueStatusBlocked", ex.Code);
+        Assert.Contains("Schedule On", ex.Message, StringComparison.Ordinal);
+        Assert.DoesNotContain("due date", ex.Message, StringComparison.OrdinalIgnoreCase);
     }
 
     [Fact]
@@ -187,6 +189,8 @@ public class WorkOrderBoardUpdateServiceTests
             }, "actor-1"));
 
         Assert.Equal("PastDueStatusBlocked", ex.Code);
+        Assert.Contains("Schedule On", ex.Message, StringComparison.Ordinal);
+        Assert.DoesNotContain("due date", ex.Message, StringComparison.OrdinalIgnoreCase);
     }
 
     [Fact]