feat: move-to-folder dialog, batch actions, reader source view, Focused/Other pivot

- MoveToFolderDialog: modal folder picker per account (excludes current)
- Wire 'Mover a...' in reader ⋯ menu + batch move (emit -1 -> dialog)
- Connect batch delete/mark-unread/flag handlers (were unconnected)
- Reader: 'Ver codigo fuente' reads .eml via MimeStorageService::readEmlFile
- Reader: 'Marcar como no leido' emits markUnreadRequested
- Pivot Focused/Other: EmailListModel::setShowFocusedOnly heuristic
  (flagged/pinned/frequent senders), reset to Focused on inbox select

src/ui/readerview.cpp

@@ -1,4 +1,5 @@
 #include "ui/readerview.h"
+#include "services/mimestorage.h"
 #include <QFont>
 #include <QDesktopServices>
 #include <QUrl>
@@ -15,6 +16,9 @@
 #include <QDateTime>
 #include <QClipboard>
 #include <QMessageBox>
+#include <QDialog>
+#include <QPlainTextEdit>
+#include <QDialogButtonBox>
 #include <QScrollBar>
 #include <QShortcut>
 #include <QFileDialog>
@@ -325,10 +329,50 @@ void ReaderView::setupUI() {
             if (item.has_value()) QApplication::clipboard()->setText(item->sender());
         }
     });
-    moreMenu->addAction("Ver código fuente", [this]() { /* TODO */ });
+    moreMenu->addAction("Ver código fuente", [this]() {
+        if (m_currentMailId < 0) return;
+        std::optional<MailItem> item = MailItemDao::findById(m_currentMailId);
+        if (!item.has_value()) return;
+        QByteArray raw;
+        if (!item->fileId().isEmpty()) {
+            MimeStorageService storage;
+            raw = storage.readEmlFile(item->fileId());
+        }
+        if (raw.isEmpty()) raw = item->rawMime();
+        if (raw.isEmpty()) {
+            QMessageBox::information(this, tr("Código fuente"),
+                tr("No hay código fuente disponible para este correo."));
+            return;
+        }
+        QDialog dlg(this);
+        dlg.setWindowTitle(tr("Código fuente"));
+        dlg.resize(760, 560);
+        QVBoxLayout *lay = new QVBoxLayout(&dlg);
+        QPlainTextEdit *view = new QPlainTextEdit(&dlg);
+        view->setReadOnly(true);
+        view->setPlainText(QString::fromUtf8(raw));
+        view->setStyleSheet("font-family: 'Consolas','Menlo',monospace; font-size: 12px;");
+        lay->addWidget(view);
+        QDialogButtonBox *buttons = new QDialogButtonBox(QDialogButtonBox::Close, &dlg);
+        connect(buttons, &QDialogButtonBox::rejected, &dlg, &QDialog::reject);
+        lay->addWidget(buttons);
+        dlg.exec();
+    });
     moreMenu->addSeparator();
-    moreMenu->addAction("Marcar como no leído", [this]() { /* TODO */ });
-    moreMenu->addAction("Marcar como spam", [this]() { /* TODO */ });
+    moreMenu->addAction("Marcar como no leído", [this]() {
+        if (m_currentMailId < 0) return;
+        auto item = MailItemDao::findById(m_currentMailId);
+        if (item.has_value()) {
+            item->setRead(false);
+            MailItemDao::update(*item);
+            emit markUnreadRequested(m_currentMailId);
+        }
+    });
+    moreMenu->addAction("Marcar como spam", [this]() {
+        if (m_currentMailId < 0) return;
+        QMessageBox::information(this, tr("Marcar como spam"),
+            tr("Función: mover a carpeta «Spam». Disponible en una próxima versión."));
+    });
     m_moreButton->setMenu(moreMenu);
     m_moreButton->setStyleSheet(
         "QToolButton { background: transparent; border: 1px solid #d1d1d6; border-radius: 4px; font-size: 16px; }"