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/models/EmailListModel.h

@@ -46,9 +46,19 @@ public:
     void setFolderId(int folderId);
     // Refresh the model from the database based on current folderId
     void refresh();
+    // Set search filter on the model
+    void setSearchFilter(const QString &filter);
+    // Set filter flags
+    void setShowUnreadOnly(bool show);
+    void setShowFlaggedOnly(bool show);
+    void setShowHasAttachments(bool show);
 
 private:
     QVector<MailItem> m_emails;
     int m_folderId{-1}; // -1 means all folders
+    QString m_searchFilter;
+    bool m_unreadOnly{false};
+    bool m_flaggedOnly{false};
+    bool m_hasAttachments{false};
 };
 #endif // EMAILLISTMODEL_H