Move models in separate projects

rag-api-models/SearchCandidateChunk.cs

@@ -0,0 +1,9 @@
+namespace Rag.Models
+{
+    public sealed class SearchCandidateChunk
+    {
+        public required RagDocumentRecord Document { get; init; }
+        public required RagChunkRecord Chunk { get; init; }
+        public double Score { get; init; }
+    }
+}