M5: Patch Deployment & Job Management

Backend:
- migrations/003_jobs_scheduling.sql: retry_next_at/last_error columns,
  pg_notify trigger for immediate job dispatch, retry index
- pm-agent-client: ApplyPatchesRequest/Response, AgentJobStatus,
  RollbackResponse types; apply_patches/job_status/rollback_job
  client methods + generic POST helper
- pm-core/models: JobStatus, JobKind, PatchJob, PatchJobHost,
  CreateJobRequest, PatchJobSummary
- pm-web/routes/jobs.rs: POST/GET /api/v1/jobs, GET /jobs/:id,
  POST /jobs/:id/cancel, POST /jobs/:id/rollback
- pm-worker/job_executor.rs: NOTIFY listener, periodic scanner,
  execute_host_job, poll_running_jobs, handle_host_failure (3-retry
  exponential backoff 1m/5m/30m), sync_job_status, retry_pending_jobs
- pm-worker/main.rs: spawn job_executor

Frontend:
- types/index.ts: PatchInfo, PatchJobHost, PatchJob, PatchJobSummary,
  CreateJobRequest interfaces
- api/client.ts: jobsApi (list/get/create/cancel/rollback),
  patchesApi (getHostPatches)
- pages/PatchDeploymentPage.tsx: 3-step MUI Stepper
  (host select → configure → result)
- pages/JobsPage.tsx: job list table, expandable per-host detail,
  cancel/rollback actions with confirm dialog, load-more pagination
- App.tsx: /jobs and /deployment routes wired to real pages

cargo check: 0 errors | vite build: 0 errors

frontend/src/pages/HostDetailPage.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useState } from 'react'
 import { useParams, useNavigate } from 'react-router-dom'
-import { Alert, Box, Button, Chip, CircularProgress, Container, Divider, Grid, Paper, Typography } from '@mui/material'
+import { Alert, Box, Button, CircularProgress, Container, Divider, Grid, Paper, Typography } from '@mui/material'
 import { ArrowBack } from '@mui/icons-material'
 import { apiClient } from '../api/client'
 
@@ -29,7 +29,7 @@ export default function HostDetailPage() {
         <Divider sx={{ mb: 2 }} />
         <Grid container spacing={2}>
           {host && Object.entries(host).map(([k, v]) => v !== null && v !== '' ? (
-            <Grid item xs={12} sm={6} md={4} key={k}>
+            <Grid size={{ xs: 12, sm: 6, md: 4 }} key={k}>
               <Typography variant="caption" color="text.secondary" display="block">{k.replace(/_/g, ' ').toUpperCase()}</Typography>
               <Typography variant="body2">{String(v)}</Typography>
             </Grid>