feat(a1): .NET 8 solution scaffold + Model + OpcodeTable loader

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

engine/Age.Engine/Model/Script.cs

@@ -0,0 +1,9 @@
+namespace Age.Engine.Model;
+public sealed class Script
+{
+    public required ScriptHeader Header { get; init; }
+    public required IReadOnlyList<Instruction> Instructions { get; init; }
+    public required IReadOnlyDictionary<int, int> IndexByOffset { get; init; }
+    public required IReadOnlyDictionary<int, string> Strings { get; init; }
+    public string GetString(int offset) => Strings.TryGetValue(offset, out var s) ? s : "";
+}