fix: persist saved idea state across navigation, fix UTC timestamp

- Dashboard: track saved ideas in React state (Set), compare against
  suggestion texts to show "✓ Salvata" persistently
- Backend: append 'Z' to saved_at ISO timestamp so JS parses as UTC
  (fixes "2h fa" bug for UTC+2 users)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/routers/content.py

@@ -493,7 +493,7 @@ def save_idea(
         "id": str(uuid.uuid4())[:8],
         "text": text,
         "note": data.get("note", ""),
-        "saved_at": datetime.utcnow().isoformat(),
+        "saved_at": datetime.utcnow().isoformat() + "Z",
         "used": False,
     }
     ideas.insert(0, new_idea)

frontend/src/components/Dashboard.jsx

@@ -15,6 +15,7 @@ export default function Dashboard() {
   const [loading, setLoading] = useState(true)
   const [suggestions, setSuggestions] = useState(null)
   const [suggestionsLoading, setSuggestionsLoading] = useState(false)
+  const [savedTexts, setSavedTexts] = useState(new Set())
 
   useEffect(() => {
     Promise.all([
@@ -38,6 +39,12 @@ export default function Dashboard() {
       setRecentPosts(posts.slice(0, 5))
       setProviderStatus(providers)
       setLoading(false)
+      // Load saved ideas to know which suggestions are already saved
+      api.get('/content/ideas').then(data => {
+        const texts = new Set((data.ideas || []).map(i => i.text))
+        setSavedTexts(texts)
+      }).catch(() => {})
+
       // Load cached suggestions (won't regenerate if already generated today)
       if (providers?.llm?.configured && chars.length > 0) {
         setSuggestionsLoading(true)
@@ -170,24 +177,29 @@ export default function Dashboard() {
                       >
                         Genera →
                       </Link>
+                      {savedTexts.has(topic) ? (
+                        <span style={{ fontSize: '0.72rem', color: 'var(--success)', fontWeight: 600 }}>
+                          ✓ Salvata
+                        </span>
+                      ) : (
                         <button
                           onClick={async () => {
                             try {
                               await api.post('/content/ideas', { text: topic })
-                            // Brief visual feedback
+                              setSavedTexts(prev => new Set([...prev, topic]))
-                            const btn = document.getElementById(`save-idea-${i}`)
-                            if (btn) { btn.textContent = '✓ Salvata'; btn.style.color = 'var(--success)' }
                             } catch {}
                           }}
-                        id={`save-idea-${i}`}
                           style={{
                             fontSize: '0.72rem', color: 'var(--ink-muted)', fontWeight: 500,
                             background: 'none', border: 'none', cursor: 'pointer', padding: 0,
                             transition: 'color 0.15s',
                           }}
+                          onMouseEnter={e => e.target.style.color = 'var(--accent)'}
+                          onMouseLeave={e => e.target.style.color = 'var(--ink-muted)'}
                         >
                           Salva idea
                         </button>
+                      )}
                     </div>
                   </div>
                 ))}