Rebrand LegacyForge to Weave Loader

Rename across entire codebase:
- LegacyForge -> WeaveLoader (identifiers, namespaces, classes, DLLs)
- LegacyForgeRuntime -> WeaveLoaderRuntime (C++ project)
- LegacyForge.API/Core/Launcher -> WeaveLoader.API/Core/Launcher (C# projects)
- [LegacyForge] -> [WeaveLoader] (log prefixes)
- legacyforge -> weaveloader (config files, log files, backup suffixes)
- Display name "Weave Loader" in README, CONTRIBUTING, LICENSE

WeaveLoader.API/Entity/EntityDefinition.cs

@@ -0,0 +1,16 @@
+namespace WeaveLoader.API.Entity;
+
+/// <summary>
+/// Fluent builder for defining entity properties.
+/// </summary>
+public class EntityDefinition
+{
+    internal float WidthValue = 0.6f;
+    internal float HeightValue = 1.8f;
+    internal int TrackingRangeValue = 80;
+
+    public EntityDefinition Width(float width) { WidthValue = width; return this; }
+    public EntityDefinition Height(float height) { HeightValue = height; return this; }
+    public EntityDefinition TrackingRange(int range) { TrackingRangeValue = range; return this; }
+    public EntityDefinition Size(float width, float height) { WidthValue = width; HeightValue = height; return this; }
+}

WeaveLoader.API/Entity/EntityRegistry.cs

@@ -0,0 +1,38 @@
+namespace WeaveLoader.API.Entity;
+
+/// <summary>
+/// Represents an entity type that has been registered with the game engine.
+/// </summary>
+public class RegisteredEntity
+{
+    public Identifier StringId { get; }
+    public int NumericId { get; }
+
+    internal RegisteredEntity(Identifier id, int numericId)
+    {
+        StringId = id;
+        NumericId = numericId;
+    }
+}
+
+/// <summary>
+/// Entity registration via the WeaveLoader registry.
+/// Accessed through <see cref="Registry.Entity"/>.
+/// </summary>
+public static class EntityRegistry
+{
+    public static RegisteredEntity Register(Identifier id, EntityDefinition definition)
+    {
+        int numericId = NativeInterop.native_register_entity(
+            id.ToString(),
+            definition.WidthValue,
+            definition.HeightValue,
+            definition.TrackingRangeValue);
+
+        if (numericId < 0)
+            throw new InvalidOperationException($"Failed to register entity '{id}'.");
+
+        Logger.Debug($"Registered entity '{id}' -> numeric ID {numericId}");
+        return new RegisteredEntity(id, numericId);
+    }
+}