feat(04-02): thumbnail PostCard e hint Unsplash in OutputReview

- PostCard: thumbnail 80x56px della cover image quando keyword e' URL
  - Rilevamento con startsWith('http')
  - object-cover, loading=lazy, onError nasconde se URL non valido
  - Posizionato dopo cover_title e prima dei metadati secondari
- OutputReview: hint discreto Unsplash sotto il box info edit inline
  - Visibile solo se unsplash_api_key_configured === false
  - Link a /impostazioni con stile amber discreto
  - Scompare automaticamente dopo configurazione Unsplash
  - Usa Link da react-router-dom (pattern codebase)

frontend/src/components/PostCard.tsx

@@ -181,6 +181,19 @@ export function PostCard({
               {post.cover_title}
             </p>
 
+            {/* Thumbnail cover image (solo se keyword e' un URL reale) */}
+            {post.cover_image_keyword.startsWith('http') && (
+              <div className="mt-2 mb-1">
+                <img
+                  src={post.cover_image_keyword}
+                  alt="Cover preview"
+                  loading="lazy"
+                  className="w-20 h-14 object-cover rounded-md border border-stone-700"
+                  onError={(e) => { (e.target as HTMLImageElement).style.display = 'none' }}
+                />
+              </div>
+            )}
+
             {/* Metadati secondari */}
             {slot && (
               <div className="flex flex-wrap gap-x-3 gap-y-0.5 mt-2">

frontend/src/pages/OutputReview.tsx

@@ -12,8 +12,8 @@
 
 import { Download, Loader2, RefreshCw } from 'lucide-react'
 import { useEffect, useState } from 'react'
-import { useParams } from 'react-router-dom'
+import { Link, useParams } from 'react-router-dom'
-import { useDownloadEditedCsv, useJobResults } from '../api/hooks'
+import { useDownloadEditedCsv, useJobResults, useSettingsStatus } from '../api/hooks'
 import { PostCard } from '../components/PostCard'
 import type { PostResult } from '../types'
 
@@ -21,6 +21,7 @@ export function OutputReview() {
   const { jobId } = useParams<{ jobId: string }>()
   const { data: jobData, isLoading, error } = useJobResults(jobId ?? null)
   const downloadMutation = useDownloadEditedCsv()
+  const { data: settingsStatus } = useSettingsStatus()
 
   // Stato locale dei post — viene aggiornato da edit inline e rigenerazione
   const [localResults, setLocalResults] = useState<PostResult[]>([])
@@ -156,6 +157,20 @@ export function OutputReview() {
         Le modifiche saranno incluse nel CSV scaricato.
       </div>
 
+      {/* Hint Unsplash — visibile solo se non configurato */}
+      {settingsStatus && !settingsStatus.unsplash_api_key_configured && (
+        <div className="px-4 py-2 rounded-lg bg-stone-800/30 border border-stone-700/50 text-xs text-stone-600 flex items-center gap-2 flex-wrap">
+          <span>Le colonne immagine contengono keyword testuali.</span>
+          <Link
+            to="/impostazioni"
+            className="text-amber-500/70 hover:text-amber-400 underline underline-offset-2 transition-colors"
+          >
+            Configura Unsplash
+          </Link>
+          <span>per URL immagini reali nel CSV.</span>
+        </div>
+      )}
+
       {/* Griglia post */}
       <div className="space-y-3">
         {localResults.length === 0 ? (