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.DSL/ShaderCompiler/DSLShaderSemantics.cs

@@ -32,6 +32,7 @@ internal class PassSemantic
     public ShaderEntryPoint meshShader;
     public ShaderEntryPoint pixelShader;
     public List<string>? defines;
+    public List<string>? includes;
     public List<KeywordsGroup>? keywords;
     public PipelineSemantic? localPipeline;
 }