Add Luna.Memory with SQLite-backed persistent memory store

Implement IMemoryStore interface and MemoryStore using EF Core with
SQLite for conversation and knowledge persistence. Includes DI
service registration extensions.

Luna.Memory/IMemoryStore.cs

@@ -0,0 +1,10 @@
+namespace Luna.Memory;
+
+/// <summary>
+/// Responsible for writes from the running agent
+/// </summary>
+public interface IMemoryStore
+{
+    Task AddMemoryAsync(string memory);
+    Task<string> GetMemoriesAsync();
+}