test: seed AssignedSite rows for partial-shift handover tests

AcceptAsync hard-fails on the partial path when no AssignedSite exists
for source/target (safety net against silent derived-field corruption).
The new partial-shift tests did not seed these rows, so CI failed with
"AssignedSite missing for source worker". Seed both sites in the shared
SeedPartialShiftPairAsync helper.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: renemadsen

eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn.Test/ContentHandoverServiceTests.cs

@@ -496,6 +496,19 @@ public async Task GetMineAsync_ReturnsRequestsFromSender()
 
     private async Task<(PlanRegistration source, PlanRegistration target)> SeedPartialShiftPairAsync(DateTime date)
     {
+        // Accept path recomputes derived fields via PlanRegistrationHelper, which
+        // requires an AssignedSite row per SdkSitId. Seed both before the plan rows.
+        if (!await TimePlanningPnDbContext.AssignedSites.AnyAsync(a => a.SiteId == 1))
+        {
+            await new AssignedSite { SiteId = 1, CreatedByUserId = 1, UpdatedByUserId = 1 }
+                .Create(TimePlanningPnDbContext);
+        }
+        if (!await TimePlanningPnDbContext.AssignedSites.AnyAsync(a => a.SiteId == 2))
+        {
+            await new AssignedSite { SiteId = 2, CreatedByUserId = 1, UpdatedByUserId = 1 }
+                .Create(TimePlanningPnDbContext);
+        }
+
         var source = new PlanRegistration
         {
             Date = date,