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/rulesmanagerdialog.h

@@ -0,0 +1,44 @@
+#pragma once
+
+#include <QDialog>
+#include <QTreeWidget>
+#include <QPushButton>
+#include <QVBoxLayout>
+#include <QHBoxLayout>
+#include "db/dao/ruledao.h"
+#include "ruleditordialog.h"
+
+class RulesManagerDialog : public QDialog
+{
+    Q_OBJECT
+
+public:
+    explicit RulesManagerDialog(qint64 accountId = -1, QWidget *parent = nullptr);
+
+signals:
+    void rulesChanged();
+
+private slots:
+    void onNewRule();
+    void onEditRule(QTreeWidgetItem* item);
+    void onDeleteRule(QTreeWidgetItem* item);
+    void onToggleEnabled(QTreeWidgetItem* item);
+    void onRunRules();
+    void onImportExport(bool import);
+    void onRuleSaved(const Rule& rule);
+    void refresh();
+
+private:
+    qint64 m_accountId;
+    QTreeWidget* m_tree;
+    QPushButton* m_btnNew;
+    QPushButton* m_btnRun;
+    QPushButton* m_btnImport;
+    QPushButton* m_btnExport;
+    QPushButton* m_btnClose;
+
+    void setupUI();
+    void loadRules();
+    void addRuleToTree(const Rule& rule);
+    Rule itemToRule(QTreeWidgetItem* item) const;
+};