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: 855124a9d9. Sections: 12. Findings: 2/7/10/4/6.

internal/api/handler/audit.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"context"
 	"net/http"
 	"strconv"
 	"strings"
@@ -11,8 +12,8 @@ import (
 
 // AuditService defines the service interface for audit event operations.
 type AuditService interface {
-	ListAuditEvents(page, perPage int) ([]domain.AuditEvent, int64, error)
-	GetAuditEvent(id string) (*domain.AuditEvent, error)
+	ListAuditEvents(ctx context.Context, page, perPage int) ([]domain.AuditEvent, int64, error)
+	GetAuditEvent(ctx context.Context, id string) (*domain.AuditEvent, error)
 }
 
 // AuditHandler handles HTTP requests for audit event operations.
@@ -49,7 +50,7 @@ func (h AuditHandler) ListAuditEvents(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	events, total, err := h.svc.ListAuditEvents(page, perPage)
+	events, total, err := h.svc.ListAuditEvents(r.Context(), page, perPage)
 	if err != nil {
 		ErrorWithRequestID(w, http.StatusInternalServerError, "Failed to list audit events", requestID)
 		return
@@ -83,7 +84,7 @@ func (h AuditHandler) GetAuditEvent(w http.ResponseWriter, r *http.Request) {
 	}
 	id = parts[0]
 
-	event, err := h.svc.GetAuditEvent(id)
+	event, err := h.svc.GetAuditEvent(r.Context(), id)
 	if err != nil {
 		ErrorWithRequestID(w, http.StatusNotFound, "Audit event not found", requestID)
 		return