Bundle the Hellion icon and Exo 2 font

Replace the inherited Chat 2 icon with the 1024×1024 Hellion logo
from the Hellion Online Media brand assets so the plugin shows
its real identity in Dalamud's plugin list. Bundle Exo 2 Variable
(SIL Open Font License 1.1) as an embedded resource together with
the OFL license text — keeps the license travelling with the font
inside the assembly as the OFL requires.

A new Configuration.UseHellionFont (default true) plus a checkbox
in the Privacy tab Appearance section route FontManager's regular
font handle through tk.AddFontFromMemory using the embedded TTF
bytes when the toggle is on; flipping it off falls back to the
existing AddFontWithFallback path so users who picked their own
system font under Settings → Fonts keep that choice.

Settings.cs now treats UseHellionFont as a font-changing setting
so toggling it triggers FontManager.BuildFonts on save without
needing a plugin reload.

ChatTwo/Ui/SettingsTabs/Privacy.cs

@@ -86,6 +86,13 @@ internal sealed class Privacy : ISettingsTab
                     Mutable.HellionThemeWindowOpacity = Math.Clamp(opacity, 0.5f, 1.0f);
                 ImGuiUtil.HelpText(HellionStrings.Theme_WindowOpacity_Help);
             }
+
+            ImGui.Spacing();
+
+            ImGuiUtil.OptionCheckbox(
+                ref Mutable.UseHellionFont,
+                HellionStrings.Theme_UseHellionFont_Name,
+                HellionStrings.Theme_UseHellionFont_Description);
         }
 
         ImGui.Spacing();