fix(m2-pr-d): thread ctx through Job/Notification/Audit services

Collapse CancelJobWithContext into CancelJob; eliminate 10 context.Background()
hits across the Job+Notification+Audit service cluster by threading ctx
through their handler-facing service interfaces.

Services (ctx-first):
- service/job.go: ListJobs, GetJob, CancelJob, ApproveJob, RejectJob now
  accept ctx; the CancelJobWithContext wrapper is removed (handler callers
  continue to invoke CancelJob, now ctx-aware).
- service/notification.go: ListNotifications, GetNotification, MarkAsRead
  accept ctx.
- service/audit.go: ListAuditEvents, GetAuditEvent accept ctx.

Handlers (interface + callsites):
- handler/jobs.go, handler/notifications.go, handler/audit.go: local
  service interfaces updated, r.Context() threaded at every callsite.

Tests:
- Mock services updated to match the new interfaces (ctx accepted and
  ignored via '_ context.Context' first parameter; Fn closure fields
  unchanged).
- job_test.go / notification_test.go callsites thread context.Background()
  to match production shape.

Verification:
  go build ./...                 ok
  go vet ./...                   ok
  go test -short ./...           ok
  go test -race -short ./...     ok
  golangci-lint run ./...        0 issues

Locked decisions from the M-2 plan:
  D-1 ctx-only signatures (no dual forms)
  D-4 preserve handler method names facing the router
  D-5 domain types stay ctx-free

Audit complete. Commit: 1f6cf0eafa. Sections: 12. Findings: 2/7/10/4/6.

internal/service/notification_test.go

@@ -370,7 +370,7 @@ func TestListNotifications(t *testing.T) {
 	}
 
 	// List with pagination
-	notifs, total, err := svc.ListNotifications(1, 3)
+	notifs, total, err := svc.ListNotifications(context.Background(), 1, 3)
 	if err != nil {
 		t.Fatalf("ListNotifications failed: %v", err)
 	}
@@ -404,7 +404,7 @@ func TestMarkAsRead(t *testing.T) {
 	notifRepo.AddNotification(notif)
 
 	// Mark as read
-	err := svc.MarkAsRead(notif.ID)
+	err := svc.MarkAsRead(context.Background(), notif.ID)
 	if err != nil {
 		t.Fatalf("MarkAsRead failed: %v", err)
 	}
@@ -434,7 +434,7 @@ func TestGetNotification(t *testing.T) {
 	notifRepo.AddNotification(notif)
 
 	// Get the notification
-	retrieved, err := svc.GetNotification(notif.ID)
+	retrieved, err := svc.GetNotification(context.Background(), notif.ID)
 	if err != nil {
 		t.Fatalf("GetNotification failed: %v", err)
 	}