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
+        );
+    }
 }

HellionChat/Integrations/IntegrationLinks.cs

@@ -1,3 +1,6 @@
+using System.Runtime.CompilerServices;
+using HellionChat.Util;
+
 namespace HellionChat.Integrations;
 
 // Third-party plugin URLs — separate from BrandingLinks (Hellion-owned URLs).
@@ -5,4 +8,13 @@ internal static class IntegrationLinks
 {
     public const string HonorificRepo = "https://github.com/Caraxi/Honorific";
     public const string HonorificAuthor = "https://github.com/Caraxi";
+
+    // See BrandingLinks.ValidateUrls for the CA2255 rationale.
+#pragma warning disable CA2255
+    [ModuleInitializer]
+#pragma warning restore CA2255
+    internal static void ValidateUrls()
+    {
+        UrlValidation.ValidateAll(nameof(IntegrationLinks), HonorificRepo, HonorificAuthor);
+    }
 }

HellionChat/Util/UrlValidation.cs

@@ -0,0 +1,23 @@
+namespace HellionChat.Util;
+
+internal static class UrlValidation
+{
+    // Used by BrandingLinks/IntegrationLinks at module init. A typo in a URL
+    // rotation throws loudly at plugin load instead of silently failing when
+    // a user clicks the broken button.
+    public static void ValidateAll(string source, params string[] urls)
+    {
+        foreach (var url in urls)
+        {
+            if (
+                !Uri.TryCreate(url, UriKind.Absolute, out var uri)
+                || (uri.Scheme is not "https" and not "http")
+            )
+            {
+                throw new InvalidOperationException(
+                    $"{source} contains malformed URL: {url}"
+                );
+            }
+        }
+    }
+}