Refactor shader system: arrays, keywords, property syntax

Major refactor of shader compiler and related systems:
- Switch ShaderDescriptor/PassDescriptor to arrays; remove IPassDescriptor
- Rewrite keywords block parser/semantic analysis for flexible syntax
- Change property initializers to brace syntax `{ ... }`
- Simplify TokenStream API (remove ref index params)
- Make GetBindlessIndex return uint (~0u for not found)
- Update shader compilation and variant logic for new descriptors
- Update test shader syntax to match new property/keyword formats
- Add AGENTS.md agent development guide
- Add Antlr4 dependency to Ghost.DSL
- Miscellaneous code style and error handling improvements

Ghost.Graphics/Core/RenderingContext.cs

@@ -116,8 +116,8 @@ public readonly unsafe ref struct RenderingContext
             localToWorld = localToWorld,
             worldBoundsMin = meshData.BoundingBox.Min,
             worldBoundsMax = meshData.BoundingBox.Max,
-            vertexBuffer = _engine.ResourceDatabase.GetBindlessIndex(meshData.VertexBuffer.AsResource()).GetValueOrThrow(),
-            indexBuffer = _engine.ResourceDatabase.GetBindlessIndex(meshData.IndexBuffer.AsResource()).GetValueOrThrow(),
+            vertexBuffer = _engine.ResourceDatabase.GetBindlessIndex(meshData.VertexBuffer.AsResource()),
+            indexBuffer = _engine.ResourceDatabase.GetBindlessIndex(meshData.IndexBuffer.AsResource()),
         };
 
         var bufferHandle = meshData.ObjectDataBuffer.AsResource();
@@ -214,8 +214,8 @@ public readonly unsafe ref struct RenderingContext
 
         var data = new PushConstantsData
         {
-            objectIndex = _engine.ResourceDatabase.GetBindlessIndex(meshRef.ObjectDataBuffer.AsResource()).GetValueOrThrow(),
-            materialIndex = _engine.ResourceDatabase.GetBindlessIndex(materialRef._cBufferCache.GpuResource.AsResource()).GetValueOrThrow(),
+            objectIndex = _engine.ResourceDatabase.GetBindlessIndex(meshRef.ObjectDataBuffer.AsResource()),
+            materialIndex = _engine.ResourceDatabase.GetBindlessIndex(materialRef._cBufferCache.GpuResource.AsResource()),
         };
 
         var pushConstantSpan = new ReadOnlySpan<uint>(&data, sizeof(PushConstantsData) / sizeof(uint));