refactor: Clean up some widths

lib/config/app_config.dart

@@ -12,7 +12,7 @@ abstract class AppConfig {
   static double fontSizeFactor = 1;
   static const Color chatColor = primaryColor;
   static Color? colorSchemeSeed = primaryColor;
-  static const double messageFontSize = 15.75;
+  static const double messageFontSize = 16.0;
   static const bool allowOtherHomeservers = true;
   static const bool enableRegistration = true;
   static const Color primaryColor = Color(0xFF5625BA);

lib/pages/chat_list/navi_rail_item.dart

@@ -33,8 +33,8 @@ class NaviRailItem extends StatelessWidget {
     return HoverBuilder(
       builder: (context, hovered) {
         return SizedBox(
-          height: 64,
-          width: 64,
+          height: FluffyThemes.navRailWidth,
+          width: FluffyThemes.navRailWidth,
           child: Stack(
             children: [
               Positioned(

lib/widgets/layouts/two_column_layout.dart

@@ -1,3 +1,4 @@
+import 'package:fluffychat/config/themes.dart';
 import 'package:flutter/material.dart';
 
 class TwoColumnLayout extends StatelessWidget {
@@ -20,7 +21,8 @@ class TwoColumnLayout extends StatelessWidget {
             Container(
               clipBehavior: Clip.antiAlias,
               decoration: const BoxDecoration(),
-              width: 360.0 + (displayNavigationRail ? 64 : 0),
+              width: FluffyThemes.columnWidth +
+                  (displayNavigationRail ? FluffyThemes.navRailWidth : 0),
               child: mainView,
             ),
             Container(