feat: IMAP sync incremental + Account Setup Wizard + robust FETCH parser

- ImapSynchronizer::syncFolder(): detecta eliminados (UIDs locales no en servidor), fetch nuevos (sinceUid), actualiza flags (FLAGS batch)
- fetchAllUids(): SELECT + SEARCH ALL para lista completa UIDs servidor
- parseAndUpdateFlags(): FETCH FLAGS en lotes 100, update DB si cambió read/flagged
- AccountSetupDialog: integra ConnectionWizard para IMAP/POP3 con test de conexión real
- IMAP FETCH parser robusto: logging respuesta servidor + fallback UID-by-UID
- Fix: FETCH failed logging muestra first/last UID + respuesta truncada

src/ui/mainmainwindow.h

@@ -42,6 +42,14 @@ private slots:
     void onProgressChanged(int percent);
     void onStatusMessage(const QString &msg);
 
+    // Slots for embedded compose view
+    void onEmbeddedSendRequested(const QString &to, const QString &cc, const QString &bcc,
+                               const QString &subject, const QString &body,
+                               const QDateTime &scheduleTime,
+                               const QString &fromAddress,
+                               const QStringList &attachmentPaths);
+    void onEmbeddedDiscardRequested();
+    void onEmbeddedDetachRequested(QWidget *widget);
 private:
     void setupUI();
     void setupSidebar();
@@ -68,6 +76,9 @@ private:
     QTreeView *m_folderTree;
     MailListView *m_mailListView;
     ReaderView *m_emailViewer;
+    QStackedWidget *m_viewerStack;
+    QWidget *m_placeholderWidget;
+    ComposeView *m_embeddedComposeView;
 
     // Other pages
     ComposeView *m_composeView;
@@ -78,12 +89,12 @@ private:
     // Services & Models
     FolderListModel *m_folderModel;
     EmailListModel *m_emailModel;
-    AccountService *m_accountService;
-    MailService *m_mailService;
+    AccountService *m_accountService = nullptr;
+    MailService *m_mailService = nullptr;
 
     QToolBar *m_toolBar;
     int m_currentFolderId;
     int m_currentMailId;
 
     QProgressBar *m_progressBar;
-};
+};