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/jobs.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"context"
 	"encoding/json"
 	"io"
 	"net/http"
@@ -13,11 +14,11 @@ import (
 
 // JobService defines the service interface for job operations.
 type JobService interface {
-	ListJobs(status, jobType string, page, perPage int) ([]domain.Job, int64, error)
-	GetJob(id string) (*domain.Job, error)
-	CancelJob(id string) error
-	ApproveJob(id string) error
-	RejectJob(id string, reason string) error
+	ListJobs(ctx context.Context, status, jobType string, page, perPage int) ([]domain.Job, int64, error)
+	GetJob(ctx context.Context, id string) (*domain.Job, error)
+	CancelJob(ctx context.Context, id string) error
+	ApproveJob(ctx context.Context, id string) error
+	RejectJob(ctx context.Context, id string, reason string) error
 }
 
 // JobHandler handles HTTP requests for job operations.
@@ -57,7 +58,7 @@ func (h JobHandler) ListJobs(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	jobs, total, err := h.svc.ListJobs(status, jobType, page, perPage)
+	jobs, total, err := h.svc.ListJobs(r.Context(), status, jobType, page, perPage)
 	if err != nil {
 		ErrorWithRequestID(w, http.StatusInternalServerError, "Failed to list jobs", requestID)
 		return
@@ -91,7 +92,7 @@ func (h JobHandler) GetJob(w http.ResponseWriter, r *http.Request) {
 	}
 	id = parts[0]
 
-	job, err := h.svc.GetJob(id)
+	job, err := h.svc.GetJob(r.Context(), id)
 	if err != nil {
 		ErrorWithRequestID(w, http.StatusNotFound, "Job not found", requestID)
 		return
@@ -119,7 +120,7 @@ func (h JobHandler) CancelJob(w http.ResponseWriter, r *http.Request) {
 	}
 	jobID := parts[0]
 
-	if err := h.svc.CancelJob(jobID); err != nil {
+	if err := h.svc.CancelJob(r.Context(), jobID); err != nil {
 		ErrorWithRequestID(w, http.StatusInternalServerError, "Failed to cancel job", requestID)
 		return
 	}
@@ -149,7 +150,7 @@ func (h JobHandler) ApproveJob(w http.ResponseWriter, r *http.Request) {
 	}
 	jobID := parts[0]
 
-	if err := h.svc.ApproveJob(jobID); err != nil {
+	if err := h.svc.ApproveJob(r.Context(), jobID); err != nil {
 		if strings.Contains(err.Error(), "not found") {
 			ErrorWithRequestID(w, http.StatusNotFound, "Job not found", requestID)
 			return
@@ -193,7 +194,7 @@ func (h JobHandler) RejectJob(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	if err := h.svc.RejectJob(jobID, body.Reason); err != nil {
+	if err := h.svc.RejectJob(r.Context(), jobID, body.Reason); err != nil {
 		if strings.Contains(err.Error(), "not found") {
 			ErrorWithRequestID(w, http.StatusNotFound, "Job not found", requestID)
 			return