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/maillistview.cpp

@@ -326,9 +326,17 @@ void MailListView::setupUI()
     connect(m_compactDelegate, &CompactMailDelegate::markUnreadRequested,
             this, &MailListView::onCompactMarkUnreadRequested);
 
-    // Same proxy model for list view (single column)
-    m_listView->setModel(m_proxyModel);
-    m_listView->setModelColumn(0); // Use first column (subject)
+    // List view uses source model (EmailListModel) directly for proper roles
+    // NOT the proxy model that wraps EmailTreeModel
+    m_listView->setModel(m_sourceModel);
+    
+    // For selection handling, we need a proxy to support single-column list view
+    m_listProxyModel = new QSortFilterProxyModel(this);
+    m_listProxyModel->setSourceModel(m_sourceModel);
+    m_listProxyModel->setFilterCaseSensitivity(Qt::CaseInsensitive);
+    m_listProxyModel->setFilterKeyColumn(-1); // Filter all columns
+    m_listView->setModel(m_listProxyModel);
+    m_listView->setModelColumn(0); // Use first column
 
     connect(m_listView->selectionModel(), &QItemSelectionModel::selectionChanged,
             this, &MailListView::onSelectionChanged);
@@ -362,6 +370,11 @@ void MailListView::setModel(EmailListModel *model)
     connect(m_treeView->verticalScrollBar(), &QScrollBar::valueChanged, this, &MailListView::onTreeViewScrolled);
     connect(m_listView->verticalScrollBar(), &QScrollBar::valueChanged, this, &MailListView::onListViewScrolled);
 
+    // Update list proxy model with new source model
+    if (m_listProxyModel) {
+        m_listProxyModel->setSourceModel(model);
+    }
+
     // Initial population
     refreshViews();
 }
@@ -375,7 +388,9 @@ void MailListView::refreshViews()
     m_treeModel->setEmails(emails);
     m_treeView->expandAll();
 
-    // List view uses same proxy model, just refresh
+    // List view uses m_listProxyModel which wraps m_sourceModel directly
+    // Just refresh the view to reflect any data changes
+    m_listProxyModel->invalidate();
     m_listView->update();
 }