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/job_handler_test.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"net/http"
@@ -21,35 +22,35 @@ type MockJobService struct {
 	RejectJobFn  func(id string, reason string) error
 }
 
-func (m *MockJobService) ListJobs(status, jobType string, page, perPage int) ([]domain.Job, int64, error) {
+func (m *MockJobService) ListJobs(_ context.Context, status, jobType string, page, perPage int) ([]domain.Job, int64, error) {
 	if m.ListJobsFn != nil {
 		return m.ListJobsFn(status, jobType, page, perPage)
 	}
 	return nil, 0, nil
 }
 
-func (m *MockJobService) GetJob(id string) (*domain.Job, error) {
+func (m *MockJobService) GetJob(_ context.Context, id string) (*domain.Job, error) {
 	if m.GetJobFn != nil {
 		return m.GetJobFn(id)
 	}
 	return nil, nil
 }
 
-func (m *MockJobService) CancelJob(id string) error {
+func (m *MockJobService) CancelJob(_ context.Context, id string) error {
 	if m.CancelJobFn != nil {
 		return m.CancelJobFn(id)
 	}
 	return nil
 }
 
-func (m *MockJobService) ApproveJob(id string) error {
+func (m *MockJobService) ApproveJob(_ context.Context, id string) error {
 	if m.ApproveJobFn != nil {
 		return m.ApproveJobFn(id)
 	}
 	return nil
 }
 
-func (m *MockJobService) RejectJob(id string, reason string) error {
+func (m *MockJobService) RejectJob(_ context.Context, id string, reason string) error {
 	if m.RejectJobFn != nil {
 		return m.RejectJobFn(id, reason)
 	}