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/Parser/PassBlock.cs

@@ -68,6 +68,7 @@ internal class PassBlock : IBlockParser<PassSyntax, PassSemantic>
         {
             name = syntax.name.lexeme,
             defines = DefinesBlock.SemanticAnalysis(syntax.defines, errors),
+            includes = IncludesBlock.SemanticAnalysis(syntax.includes, errors),
             keywords = KeywordsBlock.SemanticAnalysis(syntax.keywords, errors),
             localPipeline = PipelineBlock.SemanticAnalysis(syntax.localPipeline, errors),
         };