P4.1: Wire desktop notifications for failed job runs

Add Service.ShouldNotifyOnFailure() (reads config under mu) and call
fyne.CurrentApp().SendNotification in the mainwindow subscriber when a
Manual/Schedule run completes with State == "Failed" and the setting is on.

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

docs/PRE-RELEASE-TASKS.md

@@ -101,7 +101,7 @@ These land together because both edit `domain/job.go` and `storage/store.go`.
 - [x] P3.5 — Queue tests
 
 ### Phase 4 — Notifications + Command browse
-- [ ] P4.1 — Failure notifications
+- [x] P4.1 — Failure notifications
 - [ ] P4.2 — Command Browse button
 
 ### Phase 5 — Icons

src/app/operations.go

@@ -170,6 +170,15 @@ func (s *Service) SetGlobalPause(paused bool) error {
 	return err
 }
 
+// ShouldNotifyOnFailure reports whether the user has enabled desktop
+// notifications for failed job runs. It reads the config under mu so it is
+// safe to call from any goroutine.
+func (s *Service) ShouldNotifyOnFailure() bool {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	return s.store.Config.NotifyOnFailure
+}
+
 // UpdateSettings validates and persists a new application configuration. The
 // loaded jobs are re-saved because the jobs directory may have changed, and log
 // cleanup runs so a tightened retention policy takes effect immediately.

src/ui/mainwindow.go

@@ -72,6 +72,15 @@ func newMainView(w fyne.Window) (fyne.CanvasObject, func(time.Duration, bool)) {
 		fyne.Do(func() {
 			if isRecorded {
 				events = append(events, recorded.Record)
+				r := recorded.Record
+				if r.State == "Failed" &&
+					(r.Trigger == "Manual" || r.Trigger == "Schedule") &&
+					svc.ShouldNotifyOnFailure() {
+					fyne.CurrentApp().SendNotification(&fyne.Notification{
+						Title:   "GoSentry: Job Failed",
+						Content: r.JobName + ": " + r.Detail,
+					})
+				}
 			}
 			if isError {
 				events = append(events, newEvent(0, "Service", "Error", errOccurred.Err.Error()))