Initial commit: LegacyForge mod loader for Minecraft Legacy Edition

SKSE-style external mod loader with zero game source modifications.
- LegacyForge.Launcher: C# console app that injects runtime DLL into game process
- LegacyForgeRuntime: C++ DLL with PDB symbol resolution, MinHook function hooking, and .NET CoreCLR hosting
- LegacyForge.Core: C# mod discovery and lifecycle management
- LegacyForge.API: Fabric-style mod API with namespaced string IDs, fluent property builders, and event system
- ExampleMod: Sample mod demonstrating block/item registration

LegacyForge.API/ModAttribute.cs

@@ -0,0 +1,41 @@
+namespace LegacyForge.API;
+
+/// <summary>
+/// Marks a class as a LegacyForge mod and provides metadata.
+/// The class must also implement <see cref="IMod"/>.
+/// </summary>
+[AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = false)]
+public sealed class ModAttribute : Attribute
+{
+    /// <summary>
+    /// The unique mod identifier (e.g. "examplemod"). Used as the default namespace
+    /// for content registered by this mod.
+    /// </summary>
+    public string Id { get; }
+
+    /// <summary>
+    /// Human-readable display name.
+    /// </summary>
+    public string Name { get; set; } = "";
+
+    /// <summary>
+    /// Semantic version string (e.g. "1.0.0").
+    /// </summary>
+    public string Version { get; set; } = "1.0.0";
+
+    /// <summary>
+    /// Mod author(s).
+    /// </summary>
+    public string Author { get; set; } = "";
+
+    /// <summary>
+    /// Short description of the mod.
+    /// </summary>
+    public string Description { get; set; } = "";
+
+    public ModAttribute(string id)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(id);
+        Id = id;
+    }
+}