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/api/handler/notification_handler_test.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"context"
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
@@ -17,21 +18,21 @@ type MockNotificationService struct {
 	MarkAsReadFn        func(id string) error
 }
 
-func (m *MockNotificationService) ListNotifications(page, perPage int) ([]domain.NotificationEvent, int64, error) {
+func (m *MockNotificationService) ListNotifications(_ context.Context, page, perPage int) ([]domain.NotificationEvent, int64, error) {
 	if m.ListNotificationsFn != nil {
 		return m.ListNotificationsFn(page, perPage)
 	}
 	return nil, 0, nil
 }
 
-func (m *MockNotificationService) GetNotification(id string) (*domain.NotificationEvent, error) {
+func (m *MockNotificationService) GetNotification(_ context.Context, id string) (*domain.NotificationEvent, error) {
 	if m.GetNotificationFn != nil {
 		return m.GetNotificationFn(id)
 	}
 	return nil, nil
 }
 
-func (m *MockNotificationService) MarkAsRead(id string) error {
+func (m *MockNotificationService) MarkAsRead(_ context.Context, id string) error {
 	if m.MarkAsReadFn != nil {
 		return m.MarkAsReadFn(id)
 	}