feat: preferences dialog, SQL formatter, and enhanced table context menu

- PreferencesDialog (Tools → Preferences, Ctrl+,): font family/size,
  word wrap, default page size, query timeout, max history, auto-commit;
  font changes apply live to all open editors via apply_settings() cascade
- CodeEditor and TableViewer now read initial values from settings singleton
- SQL formatter (≡ Format button): uses sqlparse to reindent and uppercase
  keywords; gracefully prompts to install sqlparse if missing
- Table viewer context menu: "Filter by this value" (populates WHERE and
  reloads), "Copy row as SQL INSERT" (ready-to-paste INSERT statements),
  renamed "Copy row" → "Copy row as TSV" for clarity

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/main_window.py

@@ -30,7 +30,8 @@ from app.ui.explain_view      import ExplainPanel
 from app.ui.user_manager      import UserManagerPanel
 from app.ui.log_viewer        import LogViewer
 from app.ui.connection_dialog import ConnectionDialog
-from app.ui.shortcuts_dialog  import ShortcutsDialog
+from app.ui.shortcuts_dialog   import ShortcutsDialog
+from app.ui.preferences_dialog import PreferencesDialog
 from app.config.connections   import load_profiles, delete_profile
 from app.config.recent_files  import load_recent, add_recent, clear_recent
 from app.models.connection_model import ConnectionProfile
@@ -184,6 +185,8 @@ class MainWindow(QMainWindow):
 
         # ── Tools ─────────────────────────────────────────────────────────────
         tools_menu = mb.addMenu("&Tools")
+        tools_menu.addAction(self._act("Preferences…", self._open_preferences, "Ctrl+,"))
+        tools_menu.addSeparator()
         tools_menu.addAction(self._act("Process List…", self._open_process_list, "Ctrl+P"))
         tools_menu.addSeparator()
         tools_menu.addAction(self._act("Import CSV / JSON…", self._open_import_dialog))
@@ -581,6 +584,18 @@ class MainWindow(QMainWindow):
             "MySQL · PostgreSQL · SQLite · SQL Server<br><br>"
             "Built with Python + PyQt6.")
 
+    def _open_preferences(self):
+        dlg = PreferencesDialog(parent=self)
+        dlg.settings_applied.connect(self._apply_settings_to_open_tabs)
+        dlg.exec()
+
+    def _apply_settings_to_open_tabs(self):
+        """Push updated settings to all currently open workspace tabs."""
+        for i in range(self._workspace.count()):
+            widget = self._workspace.widget(i)
+            if hasattr(widget, "apply_settings"):
+                widget.apply_settings()
+
     def _show_shortcuts(self):
         dlg = ShortcutsDialog(parent=self)
         dlg.exec()