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/ChatTwo.csproj

@@ -43,6 +43,20 @@
          + HellionStrings.<lang>.resx) is picked up automatically by the SDK
          default include. Designer.cs is hand-maintained, no auto-gen needed. -->
 
+    <!-- Bundled Hellion font (Exo 2, OFL-1.1). Embedded as a manifest
+         resource with a fixed LogicalName so FontManager can pull the
+         bytes back at runtime via AddFontFromMemory. The OFL license
+         text travels with it inside the assembly to satisfy the
+         "license must be distributed with the font" clause. -->
+    <ItemGroup>
+        <EmbeddedResource Include="Resources\HellionFont.ttf">
+            <LogicalName>HellionFont.ttf</LogicalName>
+        </EmbeddedResource>
+        <EmbeddedResource Include="Resources\HellionFont-OFL.txt">
+            <LogicalName>HellionFont-OFL.txt</LogicalName>
+        </EmbeddedResource>
+    </ItemGroup>
+
 
     <ItemGroup>
       <Folder Include="images\" />