feat: responsive compact mail view + folder unread badges

- CompactMailDelegate: card-based view for narrow panels (<420px)
  * Avatar with hash-based color, sender + date (relative format)
  * Subject line with attachment icon
  * Action buttons: flag, delete, category, more (context menu)
  * Unread highlight with light blue background + bold sender
- MailListView: automatic switch between tree/table (wide) and list/cards (narrow)
  * QStackedWidget with QTreeView + QListView sharing same proxy model
  * resizeEvent threshold at 420px
  * Signals forwarded to MainMainWindow for actions
- FolderTreeDelegate: custom paint for folder tree
  * Unread count badge (blue pill) right-aligned on folder nodes
  * Account nodes bold, folder nodes normal weight
  * Proper indentation per depth level
- MailItemDao::countUnreadByFolderId() for real-time unread counts
- MainMainWindow handlers for compact actions (flag, delete, category, more menu)

test/test_delete_account.cpp

@@ -0,0 +1,74 @@
+#include <QCoreApplication>
+#include <QDebug>
+#include "accountservice.h"
+#include "accountdao.h"
+#include "databasemanager.h"
+#include "account.h"
+
+int main(int argc, char *argv[])
+{
+    QCoreApplication app(argc, argv);
+    // Ensure DB is initialized
+    DatabaseManager::instance().database();
+
+    AccountService service;
+
+    // Create a test account
+    Account testAcc;
+    testAcc.setEmail("test_delete@example.com");
+    testAcc.setDisplayName("Test Delete");
+    testAcc.setType(AccountType::IMAP);
+    Account::ConnectionSettings settings;
+    settings.incomingHost = "imap.example.com";
+    settings.incomingPort = 993;
+    settings.incomingSsl = true;
+    settings.outgoingHost = "smtp.example.com";
+    settings.outgoingPort = 465;
+    settings.outgoingSsl = true;
+    settings.username = "testdelete@example.com";
+    settings.password = "testpass";
+    settings.authMethod = "LOGIN";
+    testAcc.setConnectionSettings(settings);
+
+    qDebug() << "Adding test account...";
+    service.addAccount(testAcc);
+    qint64 addedId = testAcc.id();
+    qDebug() << "Added account ID:" << addedId;
+
+    // Verify exists
+    QVector<Account> accounts = AccountDao::findAll();
+    bool found = false;
+    for (const Account &acc : accounts) {
+        if (acc.email() == "test_delete@example.com") {
+            found = true;
+            qDebug() << "Found account after add, ID:" << acc.id();
+            break;
+        }
+    }
+    if (!found) {
+        qWarning() << "Account not found after add!";
+        return 1;
+    }
+
+    // Remove account
+    qDebug() << "Removing account ID:" << addedId;
+    service.removeAccount(addedId);
+
+    // Verify removed
+    accounts = AccountDao::findAll();
+    bool stillThere = false;
+    for (const Account &acc : accounts) {
+        if (acc.email() == "test_delete@example.com") {
+            stillThere = true;
+            qDebug() << "Account still present after removal!";
+            break;
+        }
+    }
+    if (stillThere) {
+        qWarning() << "FAIL: Account still present after removal.";
+        return 1;
+    } else {
+        qDebug() << "SUCCESS: Account removed successfully.";
+        return 0;
+    }
+}