Refactor render graph & DSL; remove material system

- Major optimization of Ghost.RenderGraph.Concept: pooled resources, zero-allocation hot paths, explicit queue types, and batch barrier APIs.
- Migrated Ghost.DSL shader compiler to ANTLR4-based parser; removed hand-written parser, added grammar files and semantic model conversion.
- Added CollectionPool/ListPool for pooled list management.
- Updated documentation for new architecture and performance.
- Removed Ghost.Shader.Concept (material/material system) from repo and solution.
- README.md replaced with a brief project statement.

Ghost.DSL/Grammar/GhostShaderLexer.g4

@@ -0,0 +1,33 @@
+lexer grammar GhostShaderLexer;
+
+// Keywords
+SHADER: 'shader';
+PROPERTIES: 'properties';
+PIPELINE: 'pipeline';
+PASS: 'pass';
+DEFINES: 'defines';
+KEYWORDS: 'keywords';
+INCLUDES: 'includes';
+GLOBAL: 'global';
+LOCAL: 'local';
+HLSL: 'hlsl';
+
+// Punctuation
+LBRACE: '{';
+RBRACE: '}';
+LPAREN: '(';
+RPAREN: ')';
+SEMICOLON: ';';
+COMMA: ',';
+EQUALS: '=';
+COLON: ':';
+
+// Literals
+STRING_LITERAL: '"' (~["\r\n] | '\\' .)* '"';
+NUMBER: [0-9]+ ('.' [0-9]+)? | '.' [0-9]+;
+IDENTIFIER: [a-zA-Z_][a-zA-Z0-9_]*;
+
+// Whitespace and Comments
+WS: [ \t\r\n]+ -> skip;
+LINE_COMMENT: '//' ~[\r\n]* -> skip;
+BLOCK_COMMENT: '/*' .*? '*/' -> skip;