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/Identifier.cs

@@ -0,0 +1,39 @@
+namespace WeaveLoader.API;
+
+/// <summary>
+/// A namespaced identifier in the form "namespace:path" (e.g. "minecraft:stone", "mymod:ruby_ore").
+/// </summary>
+public readonly record struct Identifier
+{
+    public string Namespace { get; }
+    public string Path { get; }
+
+    public Identifier(string ns, string path)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(ns);
+        ArgumentException.ThrowIfNullOrWhiteSpace(path);
+        Namespace = ns;
+        Path = path;
+    }
+
+    public Identifier(string id)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(id);
+
+        var colonIndex = id.IndexOf(':');
+        if (colonIndex < 0)
+        {
+            Namespace = "minecraft";
+            Path = id;
+        }
+        else
+        {
+            Namespace = id[..colonIndex];
+            Path = id[(colonIndex + 1)..];
+        }
+    }
+
+    public override string ToString() => $"{Namespace}:{Path}";
+
+    public static implicit operator Identifier(string id) => new(id);
+}