feat: complete settings view + signatures + signatures DAO + icons

- SettingsView: complete UI with tabs for Accounts, Categories, Rules, Templates, Signatures, General, Appearance
- Categories: QTreeWidget with hierarchical view, color picker, parent categories
- Rules: QListWidget with RuleEditorDialog integration, toggle enabled
- Templates: QListWidget with TemplateEditorDialog integration
- Signatures: QListWidget with SignatureEditorDialog integration
- SignatureDao: full CRUD with default signature support
- common_structs.h: QColor for Category, all structs centralized
- icons.qrc: updated with Linear/Outline/Bold icons from resources
- Category: QColor instead of QString for color
- EmailTreeModel/DateGroupProxyModel: email grouping by date
- MailListView: QTreeView with date grouping combo
- ReaderView: subject frame with shadow, avatar in header, body inside header
- MainWindow: frameless with rounded corners, 1px border, edge resize, no status bar
- icons.qrc: complete icon set from resources/icons/SVG

src/ui/settingsview.h

@@ -12,7 +12,12 @@
 #include <QRadioButton>
 #include <QButtonGroup>
 #include <QVariant>
+#include <QTreeWidget>
+#include <QLineEdit>
+#include <QDialog>
+#include <QColorDialog>
 #include "services/accountservice.h"
+#include "db/dao/common_structs.h"
 
 class SettingsView : public QWidget {
     Q_OBJECT
@@ -29,6 +34,26 @@ signals:
     void accountDeleteRequested(int accountId);
     void themeChanged(const QString &theme);
     void settingChanged(const QString &key, const QVariant &value);
+    
+    // Categories
+    void categoryAddRequested(const Category &cat);
+    void categoryEditRequested(const Category &cat);
+    void categoryDeleteRequested(qint64 categoryId);
+    
+    // Rules
+    void ruleAddRequested(const Rule &rule);
+    void ruleEditRequested(const Rule &rule);
+    void ruleDeleteRequested(qint64 ruleId);
+    
+    // Templates
+    void templateAddRequested(const Template &tmpl);
+    void templateEditRequested(const Template &tmpl);
+    void templateDeleteRequested(qint64 templateId);
+    
+    // Signatures
+    void signatureAddRequested(const Signature &sig);
+    void signatureEditRequested(const Signature &sig);
+    void signatureDeleteRequested(qint64 signatureId);
 
 private slots:
     void onAccountListChanged();
@@ -36,12 +61,58 @@ private slots:
     void onEditClicked();
     void onDeleteClicked();
     void onAccountSelectionChanged();
+    
+    // Categories
+    void onCategorySelectionChanged();
+    void onCategoryAddClicked();
+    void onCategoryEditClicked();
+    void onCategoryDeleteClicked();
+    
+    // Rules
+    void onRuleSelectionChanged();
+    void onRuleAddClicked();
+    void onRuleEditClicked();
+    void onRuleDeleteClicked();
+    void onRuleToggleEnabled();
+    
+    // Templates
+    void onTemplateSelectionChanged();
+    void onTemplateAddClicked();
+    void onTemplateEditClicked();
+    void onTemplateDeleteClicked();
+    
+    // Signatures
+    void onSignatureSelectionChanged();
+    void onSignatureAddClicked();
+    void onSignatureEditClicked();
+    void onSignatureDeleteClicked();
 
 private:
     void setupUI();
     QWidget* createAccountsTab();
     QWidget* createGeneralTab();
     QWidget* createAppearanceTab();
+    QWidget* createCategoriesTab();
+    QWidget* createRulesTab();
+    QWidget* createTemplatesTab();
+    QWidget* createSignaturesTab();
+    
+    // Category helpers
+    void loadCategories();
+    void refreshCategoryTree();
+    QTreeWidgetItem* createCategoryTreeItem(const Category &cat, QTreeWidgetItem *parent = nullptr);
+    
+    // Rule helpers
+    void loadRules();
+    QString ruleToString(const Rule &rule) const;
+    
+    // Template helpers
+    void loadTemplates();
+    QString templateToString(const Template &tmpl) const;
+    
+    // Signature helpers
+    void loadSignatures();
+    QString signatureToString(const Signature &sig) const;
 
     QTabWidget *m_tabWidget;
     QListWidget *m_accountList;
@@ -53,4 +124,29 @@ private:
 
     AccountService *m_accountService;
     int m_selectedAccountId;
+
+    // Categories
+    QTreeWidget *m_categoryTree;
+    QPushButton *m_categoryAddBtn;
+    QPushButton *m_categoryEditBtn;
+    QPushButton *m_categoryDeleteBtn;
+    
+    // Rules
+    QListWidget *m_ruleList;
+    QPushButton *m_ruleAddBtn;
+    QPushButton *m_ruleEditBtn;
+    QPushButton *m_ruleDeleteBtn;
+    QPushButton *m_ruleToggleBtn;
+    
+    // Templates
+    QListWidget *m_templateList;
+    QPushButton *m_templateAddBtn;
+    QPushButton *m_templateEditBtn;
+    QPushButton *m_templateDeleteBtn;
+    
+    // Signatures
+    QListWidget *m_signatureList;
+    QPushButton *m_signatureAddBtn;
+    QPushButton *m_signatureEditBtn;
+    QPushButton *m_signatureDeleteBtn;
 };