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.Graphics/RHI/IResourceDatabase.cs

@@ -20,7 +20,7 @@ public interface IResourceDatabase : IDisposable
     /// <summary>
     /// Imports an external unmanaged resource and returns a handle for use within the resource management system.
     /// </summary>
-    /// <typeparam name="T">The type of the unmanaged resource pointer to import.</typeparam>
+    /// <typeparam name="T">The space of the unmanaged resource pointer to import.</typeparam>
     /// <param name="resourcePtr">A pointer to the external unmanaged resource to be imported. Must remain valid for the duration of the resource's usage.</param>
     /// <param name="initialState">The initial state to assign to the imported resource.</param>
     /// <returns>A handle representing the imported resource, which can be used for subsequent operations.</returns>