ui(settings): adapt left category rail width to UI scale and make theme editor responsive #1653

Problem

1. In lib/features/settings/preferences_dialog.dart (line 377):

   // Left Category Rail
   material.Container(
     width: 184,

   The width is hardcoded to 184 without context.scaled(184). When UI scale is set to 125% or 150%, fonts, icons and search badge counts scale up, causing longer category titles ("Appearance", "SQL & Editor", "About & Storage") to truncate or awkwardly wrap onto two lines, breaking the tile alignment.
2. In lib/features/settings/theme_editor_dialog.dart (lines 157–160):

   content: material.SizedBox(
     width: 540,
     height: 480,

   Fixed dimensions are used without applying WindowLayout.dialogConstraints(context). On compact laptop screens or when vertical space is restricted, 480px + dialog header + action buttons can exceed screen height and overflow.

Solution

• Use width: context.scaled(184) for the category rail in preferences_dialog.dart.
• Apply WindowLayout.dialogConstraints(context, maxWidth: 580, maxHeight: 600) to ThemeEditorDialog to keep it responsive to viewport bounds.