feat(window): restore the title-bar, hide-button, and 24-hour-clock toggles

Re-wires four 1.5.6 settings that survived the v1.6.0 rewrite as dormant config
fields but lost their UI + consumers:
- ShowTitleBar / ShowPopOutTitleBar: gate ImGuiWindowFlags.NoTitleBar on the main
  window (ResolveFlags) and pop-out windows (new PreDraw). Inverted logic matches
  1.5.6 (flag set only when the toggle is off).
- ShowHideButton: gate the input-bar hide button on the toggle.
- Use24HourClock: add the toggle (MessageList already consumes the field).
New 'Window style' section in WindowTab; Use24HourClock in ChatTab display modes.
MainWindowFlagsStep extended with the NoTitleBar fresh-base contract.

HellionChat/Ui/Components/Settings/Tabs/ChatTab.cs

@@ -38,6 +38,11 @@ internal sealed class ChatTab
                 () => Plugin.Config.HideSameTimestamps,
                 v => Plugin.Config.HideSameTimestamps = v
             );
+            DrawToggle(
+                "24-hour clock",
+                () => Plugin.Config.Use24HourClock,
+                v => Plugin.Config.Use24HourClock = v
+            );
             DrawWorldSuffixCombo();
             DrawNameFormCombo();
         }