feat: comprehensive Wino Mail updates

- ReaderView: complete rewrite with CSS styling, headers, attachments, zoom, find, dark mode, image blocking
- Categories: DAO + UI tree widget with colors, nested categories, assignment
- Rules engine: DAO + evaluation + actions (move, mark read, flag, delete, category, forward)
- Templates: DAO + editor + manager with variables support
- Signatures: DAO + manager + auto-per-account + manual selector in compose
- ComposeView: signature combo, template selector, auto-signature on new email
- MainWindow: frameless with rounded corners, 1px border, resize from edges, no status bar
- Database: new tables (Category, MailCategory, Rule, Template, Signature) with indexes

src/ui/mainmainwindow.h

@@ -9,6 +9,11 @@
 #include <QProgressBar>
 #include <QToolBar>
 #include <QAction>
+#include <QToolButton>
+#include <QLabel>
+#include <QHBoxLayout>
+#include <QMouseEvent>
+#include <QWindowStateChangeEvent>
 
 #include "ui/readerview.h"
 #include "ui/maillistview.h"
@@ -18,6 +23,8 @@
 #include "ui/calendarview.h"
 #include "ui/models/FolderListModel.h"
 #include "ui/models/EmailListModel.h"
+#include "ui/categorytreewidget.h"
+#include "ui/templatesmanagerdialog.h"
 #include "services/accountservice.h"
 #include "services/mailservice.h"
 
@@ -28,12 +35,22 @@ public:
     explicit MainMainWindow(QWidget *parent = nullptr);
     ~MainMainWindow() override = default;
 
+protected:
+    // Frameless window handling
+    void mousePressEvent(QMouseEvent *event) override;
+    void mouseMoveEvent(QMouseEvent *event) override;
+    void mouseReleaseEvent(QMouseEvent *event) override;
+    bool nativeEvent(const QByteArray &eventType, void *message, qintptr *result) override;
+    void changeEvent(QEvent *event) override;
+
 private slots:
     void onNavChanged(int index);
     void onFolderSelected(const QModelIndex &index);
     void onEmailSelected(int mailId);
     void onComposeRequested();
-    void onReaderReplyRequested(const MailItem *item);
+    void onReaderReplyRequested(int mailId);
+    void onReaderForwardRequested(int mailId);
+    void onReaderDeleteRequested(int mailId);
     void onNewMessage();
     void openMailInIndependentWindow(int mailId);
     void onAddAccountRequested();
@@ -41,6 +58,20 @@ private slots:
     void onAccountDeleteRequested(int accountId);
     void onProgressChanged(int percent);
     void onStatusMessage(const QString &msg);
+    void onSyncRequested();
+    void onSettingsRequested();
+    void updateMaximizeButtonIcon();
+    void onCategorySelected(const Category& cat);
+    void onCategoryDoubleClicked(const Category& cat);
+    void onAssignCategoryRequested(qint64 mailId, qint64 categoryId);
+    void onCategoryCreated(const Category& cat);
+    void onCategoryEdited(const Category& cat);
+    void onCategoryDeleted(qint64 categoryId);
+    void onRulesChanged();
+    void onRunRulesOnFolder();
+    void onRunRulesOnSelected();
+    void showRulesManager();
+    void showTemplatesManager();
 
     // Slots for embedded compose view
     void onEmbeddedSendRequested(const QString &to, const QString &cc, const QString &bcc,
@@ -55,8 +86,12 @@ private:
     void setupSidebar();
     void setupMailPage();
     void connectModels();
-    void createToolBar();
+    void createTitleBar();
     void switchToPage(int pageIndex);
+    QWidget *createTitleButton(const QString &iconName, const QString &tooltip, std::function<void()> slot);
+    QWidget *createWindowControlButton(const QString &iconName, const QString &tooltip, std::function<void()> slot);
+    void updateCategoryTreeForAccount(qint64 accountId);
+    void assignCategoryToSelectedMails(qint64 categoryId);
 
     // Navigation
     QListWidget *m_sidebar;
@@ -74,6 +109,7 @@ private:
     QWidget *m_mailPage;
     QSplitter *m_folderSplitter;
     QTreeView *m_folderTree;
+    CategoryTreeWidget *m_categoryTree;
     MailListView *m_mailListView;
     ReaderView *m_emailViewer;
     QStackedWidget *m_viewerStack;
@@ -92,7 +128,20 @@ private:
     AccountService *m_accountService = nullptr;
     MailService *m_mailService = nullptr;
 
-    QToolBar *m_toolBar;
+    // Frameless title bar
+    QWidget *m_titleBar;
+    QToolButton *m_maximizeButton;
+    QToolButton *m_closeButton;
+    QPoint m_dragPos;
+    bool m_dragging = false;
+    Qt::WindowStates m_lastWindowState;
+    
+    // Resize handling (item 3)
+    QPoint m_resizeStartPos;
+    QRect m_resizeStartGeom;
+    bool m_resizing = false;
+    Qt::Edges m_resizeEdges = Qt::Edges();
+
     int m_currentFolderId;
     int m_currentMailId;