fix(v0.5.0): defaults and coupling issues from first walkthrough

- Configuration.cs: ShowTitleBar defaults to true so a fresh install
  shows the window header instead of leaving the user without a drag
  handle and hide button
- Configuration.cs: MaxLinesToRender default drops from 10000 to 5000
  to match the slider's intended ceiling and the previous user-tuned
  baseline
- ChatLogWindow.cs: 24h-clock checkbox now actually flips the format.
  The Bestand path passed null culture which on a German system
  locale always rendered 24h regardless of the toggle
- Appearance.cs + ChatLogWindow.cs + Popout.cs: when Hellion theme is
  enabled the global theme opacity drives the chat-window BgAlpha and
  the legacy WindowAlpha slider is disabled, so the two opacity
  controls no longer fight each other
- Appearance.cs: ticking UseHellionFont now flips FontsEnabled off so
  the two mutually-exclusive font stacks no longer appear active at
  the same time

ChatTwo/Ui/ChatLogWindow.cs

@@ -451,7 +451,9 @@ public sealed class ChatLogWindow : Window
             Flags |= ImGuiWindowFlags.NoTitleBar;
 
         if (LastViewport == ImGuiHelpers.MainViewport.Handle && !WasDocked)
-            BgAlpha = Plugin.Config.WindowAlpha / 100f;
+            BgAlpha = Plugin.Config.HellionThemeEnabled
+                ? Plugin.Config.HellionThemeWindowOpacity
+                : Plugin.Config.WindowAlpha / 100f;
 
         LastViewport = ImGui.GetWindowViewport().Handle;
         WasDocked = ImGui.IsWindowDocked();
@@ -1188,7 +1190,13 @@ public sealed class ChatLogWindow : Window
                 if (tab.DisplayTimestamp)
                 {
                     var localTime = message.Date.ToLocalTime();
-                    var timestamp = localTime.ToString("t", !Plugin.Config.Use24HourClock ? null : CultureInfo.CreateSpecificCulture("de-DE"));
+                    // Force the format explicitly per setting. Relying on the
+                    // current culture meant a German system locale always
+                    // produced 24h regardless of the toggle, so the checkbox
+                    // looked dead.
+                    var timestamp = Plugin.Config.Use24HourClock
+                        ? localTime.ToString("HH:mm", CultureInfo.InvariantCulture)
+                        : localTime.ToString("h:mm tt", CultureInfo.InvariantCulture);
                     if (isTable)
                     {
                         if (!Plugin.Config.HideSameTimestamps || timestamp != lastTimestamp)