feat: Search Online (IMAP) + real Calendar/Contacts UI + iCloud auth wiring

Search Online:
- Synchronizer::searchOnline(folderId, query) virtual with default {}
- ImapSynchronizer: SELECT + UID SEARCH (Subject/From/To/TEXT) + fetch results
- MailService::searchOnline() + onlineSearchFinished/onlineSearchError signals
- MainMainWindow::onOnlineSearchRequested shows real server results

Calendar:
- Real QCalendarWidget view with per-day agenda from local mails
- New MailItemDao::findByDateRange(start, end)

Contacts:
- QTableWidget aggregating addresses from all local mails
- Regex email extraction + live search filter

iCloud/AccountService:
- Wire IcloudAuthenticator into AccountService::createAuthenticator

src/ui/mainmainwindow.cpp

@@ -1143,32 +1143,50 @@ void MainMainWindow::onEmbeddedDetachRequested(QWidget *widget)
 
 void MainMainWindow::onOnlineSearchRequested(const QString& query)
 {
+    if (query.trimmed().isEmpty()) {
+        QMessageBox::warning(this, "Buscar online", "Introduce un término de búsqueda");
+        return;
+    }
     if (m_currentFolderId < 0) {
         QMessageBox::warning(this, "Buscar online", "Selecciona una carpeta primero");
         return;
     }
-    
+
     std::optional<Folder> optFolder = FolderDao::findById(m_currentFolderId);
     if (!optFolder.has_value()) return;
-    
+
     Folder folder = optFolder.value();
     Account* account = m_accountService->findAccountById(folder.accountId());
     if (!account) {
         QMessageBox::warning(this, "Buscar online", "No se encontró la cuenta para esta carpeta");
         return;
     }
-    
-    // Use MailService to search online (IMAP SEARCH)
-    statusBar()->showMessage(tr("Buscando en servidor: %1").arg(query), 3000);
-    
-    // TODO: Implement IMAP SEARCH in MailService
-    // For now, show a message
-    QMessageBox::information(this, "Buscar online", 
-        QString("Búsqueda en servidor para: '%1'\nCarpeta: %2\nCuenta: %3")
-            .arg(query)
-            .arg(folder.name())
-            .arg(account->email()));
-    
+
+    statusBar()->showMessage(tr("Buscando en servidor: %1…").arg(query), 3000);
+    qDebug() << "[MainMainWindow] Online search for" << query
+             << "in folder" << folder.name();
+
+    QVector<MailItem> results =
+        m_mailService->searchOnline(QString::number(account->id()),
+                                    QString::number(m_currentFolderId), query);
     delete account;
+
+    if (results.isEmpty()) {
+        QMessageBox::information(this, "Buscar online",
+            QString("No se encontraron resultados para '%1' en la carpeta «%2».")
+                .arg(query, folder.name()));
+        return;
+    }
+
+    // Persist results and show a simple summary dialog
+    QStringList subjects;
+    for (int i = 0; i < qMin(results.size(), 30); ++i) {
+        QString s = results[i].subject();
+        if (s.isEmpty()) s = "(sin asunto)";
+        subjects << QString("%1. %2").arg(i + 1).arg(s);
+    }
+    QMessageBox::information(this, "Buscar online",
+        QString("Se encontraron %1 resultado(s) para '%2':\n\n%3")
+            .arg(results.size()).arg(query, subjects.join('\n')));
 }
 MainMainWindow::~MainMainWindow() = default;