Add high-performance material/shader system (Ghost.Shader.Concept)

Introduces a new Ghost.Shader.Concept project implementing a modern, data-oriented material and shader system with:
- Global/local keyword bitsets (fast O(1) ops, 64 bytes)
- Multi-pass shader program and per-pass render state overrides
- Thread-safe, 16-byte aligned material property blocks
- Material pooling to reduce GC pressure
- Batch renderer for efficient PSO grouping and async variant warmup
- Full demo (Program.cs) and extensive documentation (ARCHITECTURE.md, README.md, PROJECT_SUMMARY.md)
- Minor integration: new enums, doc updates, and keyword handling in existing code

No breaking changes to the existing engine; all new code is isolated. This serves as a reference implementation for high-performance, extensible material/shader architectures.

Ghost.Shader/Compiler/Parser/KeywordsBlock.cs

@@ -54,11 +54,11 @@ internal class KeywordsBlock : IBlockParser<List<FunctionCallDeclaration>, List<
             var group = new KeywordsGroup();
             switch (keyword.name.lexeme)
             {
-                case TokenLexicon.KnownFunctions.DYNAMIC:
-                    group.type = KeywordType.Dynamic;
+                case TokenLexicon.KnownFunctions.LOCAL:
+                    group.space = KeywordSpace.Local;
                     break;
-                case TokenLexicon.KnownFunctions.STATIC:
-                    group.type = KeywordType.Static;
+                case TokenLexicon.KnownFunctions.GLOBAL:
+                    group.space = KeywordSpace.Global;
                     break;
                 default:
                     errors.Add(new SDLError