feat(branding): validate URL constants on module init (F11.2)

BrandingLinks (5 Hellion-owned URLs) and IntegrationLinks (2 third-party
plugin URLs) now run through UrlValidation.ValidateAll from a
[ModuleInitializer] hook. A malformed URL throws InvalidOperationException
at plugin load with the source class and the broken URL in the message,
instead of silently failing when a user clicks the button.

CA2255 is suppressed at the attribute sites — the warning is for library
code shipped to unknown consumers, but the plugin DLL is loaded directly
by Dalamud, which makes module-init the right one-shot hook.

HellionChat/Branding/BrandingLinks.cs

@@ -1,3 +1,6 @@
+using System.Runtime.CompilerServices;
+using HellionChat.Util;
+
 namespace HellionChat.Branding;
 
 // Centralised — a future invite/URL rotation only touches this file.
@@ -9,4 +12,22 @@ internal static class BrandingLinks
         "https://gitea.hellion-forge.cloud/JonKazama-Hellion/HellionChat";
     public const string HellionForgeWebsite = "https://hellion-forge.cloud";
     public const string HellionMediaWebsite = "https://hellion-media.de/de";
+
+    // CA2255 warns against [ModuleInitializer] in library code, but Dalamud
+    // loads the plugin DLL directly so the module-init pass is the right hook
+    // for a one-shot URL sanity check at plugin load.
+#pragma warning disable CA2255
+    [ModuleInitializer]
+#pragma warning restore CA2255
+    internal static void ValidateUrls()
+    {
+        UrlValidation.ValidateAll(
+            nameof(BrandingLinks),
+            HellionForgeDiscordInvite,
+            HellionForgeGitea,
+            HellionChatRepo,
+            HellionForgeWebsite,
+            HellionMediaWebsite
+        );
+    }
 }