Apply Hellion theme plugin-wide with multi-accent palette

Move from a local color stack inside Hellion-only surfaces to a
single push wrapping Plugin.Draw, so chat log, settings,
viewers, the file dialog and the wizard all render under the same
palette. The local Push() helper stays for explicit use, but the
two existing call sites (Privacy tab, FirstRunWizard) now drop
their local pushes — the global stack already covers them and
double-pushing would shift colors on every frame.

Palette grew from a single cyan accent into a three-tone HUD set:

  Primary cyan-teal (#00B8D4)  → buttons, checkboxes, slider grabs,
                                 separator hover/active.
  Secondary industrial amber   → scrollbar grab and resize-grip
  (#FFB300)                      hover/active highlights.
  Tertiary slate violet         → active title bars and active tabs
  (#7B61FF)                      so identity beats out the cyan
                                 accent without competing with it on
                                 action controls.

Surfaces are deep slate (#0E1A20 windows, #102027 children, #162831
frames) with steel borders (#37474F). Style variables flatten the
default Dalamud rounding into something more geometric: 4 px window
rounding, 2 px frame/grab/tab/scrollbar, 1 px borders.

A new Configuration.HellionThemeEnabled (default true) and a
matching Appearance section at the top of the Privacy tab let users
turn the whole thing off and fall back to the Dalamud default look.
The flag is checked once per frame in Plugin.Draw — `using
IDisposable? _ = ... ? PushGlobal() : null` — so disabling has zero
overhead beyond a bool check.

ChatTwo/Resources/HellionStrings.Designer.cs

@@ -130,4 +130,8 @@ internal class HellionStrings
     internal static string Export_Success => Get(nameof(Export_Success));
     internal static string Export_Empty => Get(nameof(Export_Empty));
     internal static string Export_Error => Get(nameof(Export_Error));
+
+    internal static string Theme_Heading => Get(nameof(Theme_Heading));
+    internal static string Theme_Enabled_Name => Get(nameof(Theme_Enabled_Name));
+    internal static string Theme_Enabled_Description => Get(nameof(Theme_Enabled_Description));
 }