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/Block/BlockRegistry.cs

@@ -0,0 +1,51 @@
+namespace LegacyForge.API.Block;
+
+/// <summary>
+/// Represents a block that has been registered with the game engine.
+/// </summary>
+public class RegisteredBlock
+{
+    /// <summary>The namespaced string ID (e.g. "mymod:ruby_ore").</summary>
+    public Identifier StringId { get; }
+
+    /// <summary>The numeric ID allocated by the engine.</summary>
+    public int NumericId { get; }
+
+    internal RegisteredBlock(Identifier id, int numericId)
+    {
+        StringId = id;
+        NumericId = numericId;
+    }
+}
+
+/// <summary>
+/// Block registration via the LegacyForge registry.
+/// Accessed through <see cref="Registry.Block"/>.
+/// </summary>
+public static class BlockRegistry
+{
+    /// <summary>
+    /// Register a new block with the game engine.
+    /// </summary>
+    /// <param name="id">Namespaced identifier (e.g. "mymod:ruby_ore").</param>
+    /// <param name="properties">Block properties built with <see cref="BlockProperties"/>.</param>
+    /// <returns>A handle to the registered block.</returns>
+    public static RegisteredBlock Register(Identifier id, BlockProperties properties)
+    {
+        int numericId = NativeInterop.native_register_block(
+            id.ToString(),
+            (int)properties.MaterialValue,
+            properties.HardnessValue,
+            properties.ResistanceValue,
+            (int)properties.SoundValue,
+            properties.IconValue,
+            properties.LightEmissionValue,
+            properties.LightBlockValue);
+
+        if (numericId < 0)
+            throw new InvalidOperationException($"Failed to register block '{id}'. No free IDs or invalid parameters.");
+
+        Logger.Debug($"Registered block '{id}' -> numeric ID {numericId}");
+        return new RegisteredBlock(id, numericId);
+    }
+}