feat: Cron management API and frontend page (Phase 5)

Backend: CRON API with list/logs/run/pause/resume endpoints, Hermes CLI
integration, system cron jobs, audit logging for operations.
Frontend: CronPage with filter bar (status/profile), table with 30s polling,
log modal with level-colored messages, action buttons (run/pause/resume),
run confirmation dialog, 4-state coverage. Sidebar shows cron failure badge.

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/api/cron.ts

@@ -0,0 +1,52 @@
+import client from './client'
+
+export interface CronJob {
+  id: string
+  job_name: string
+  profile: string
+  schedule: string
+  status: string
+  last_run: string | null
+  last_run_success: boolean | null
+  success_rate: number
+  has_logs: boolean
+  system: boolean
+  consecutive_failures: number
+}
+
+export interface CronListResponse {
+  jobs: CronJob[]
+  has_failures: boolean
+}
+
+export interface CronLogItem {
+  time: string
+  status: string
+  message: string
+}
+
+export interface CronLogsResponse {
+  logs: CronLogItem[]
+}
+
+export interface CronActionResponse {
+  success: boolean
+  action: string
+  job_id: string
+  detail: string
+}
+
+export const getCronJobs = (params?: { status?: string; profile?: string }) =>
+  client.get<CronListResponse>('/cron/jobs', { params })
+
+export const getCronLogs = (jobId: string) =>
+  client.get<CronLogsResponse>(`/cron/jobs/${jobId}/logs`)
+
+export const runCronJob = (jobId: string) =>
+  client.post<CronActionResponse>(`/cron/jobs/${jobId}/run`)
+
+export const pauseCronJob = (jobId: string) =>
+  client.post<CronActionResponse>(`/cron/jobs/${jobId}/pause`)
+
+export const resumeCronJob = (jobId: string) =>
+  client.post<CronActionResponse>(`/cron/jobs/${jobId}/resume`)