feat: add daily cron to apply scheduled default hours changes

Add ApplyScheduledDefaultHours which checks default_hours_scheduled_changes at midnight, bulk-updates working_hours with staged values, and inserts an admin_notification. Register as the 'apply-default-hours' job in the scheduler (daily at 00:05).

backend/internal/jobs/cleanup.go

@@ -133,6 +133,16 @@ func RegisterAll(s *Scheduler) {
 		Handler:     scheduling.CleanupOldNameHistory,
 	})
 
+	// === STAGED HOURS CHANGE ===
+
+	s.Register(Job{
+		Name:        "apply-default-hours",
+		Schedule:    "5 0 * * *",          // Daily at 00:05 — after midnight to avoid race
+		Timeout:     30 * time.Second,
+		Concurrency: 1,
+		Handler:     scheduling.ApplyScheduledDefaultHours,
+	})
+
 	// === BUSINESS LOGIC JOBS ===
 
 	s.Register(Job{

backend/internal/jobs/scheduler_test.go

@@ -407,17 +407,14 @@ func TestColoredRows_Reset(t *testing.T) {
 // RegisterAll Tests
 // ============================================================
 
-// TestRegisterAll_RegistersExpectedJobs verifies RegisterAll registers exactly 19 jobs
-// with all required fields populated (non-empty Name, non-empty Schedule, non-nil
-// Handler, positive Timeout).
 func TestRegisterAll_RegistersExpectedJobs(t *testing.T) {
 	t.Parallel()
 
 	s := New()
 	RegisterAll(s)
 
-	if got := len(s.registry); got != 19 {
-		t.Fatalf("RegisterAll() registered %d jobs, want 19", got)
+	if got := len(s.registry); got != 20 {
+		t.Fatalf("RegisterAll() registered %d jobs, want 20", got)
 	}
 
 	registered := make(map[string]Job, len(s.registry))
@@ -490,6 +487,7 @@ func expectedJobNames() map[string]bool {
 		"transition-discount-campaigns":       true,
 		"cleanup-verification-codes":          true,
 		"cleanup-refresh-tokens":              true,
+		"apply-default-hours":                 true,
 	}
 }