Move RAG repository from rag-api to rag-data — consolidate data layer ownership

- Move IRagRepository, EfRagRepository, and VectorSerializer from rag-api/Data to rag-data/Repositories
- Add rag-api-models ProjectReference to rag-data.csproj for model type availability
- Delete rag-api/Data folder (no longer needed; all data access is now in rag-data)
- This aligns RAG with email-api and other services: all data code in the data project

Pattern: rag-api (API logic) → rag-data (repository, EF entities, migrations)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Apis/rag-data/Repositories/Contracts/IRagRepository.cs

@@ -0,0 +1,16 @@
+using Rag.Models;
+
+namespace Rag.Data.Repositories.Contracts;
+
+public interface IRagRepository
+{
+    Task InitializeAsync(CancellationToken ct);
+    Task<RagDocumentRecord?> GetDocumentByTextHashAsync(string textHash, string? sourceUrl, CancellationToken ct);
+    Task<RagDocumentRecord?> GetDocumentByIdAsync(string id, CancellationToken ct);
+    Task SaveDocumentAsync(RagDocumentRecord document, IReadOnlyList<RagChunkRecord> chunks, CancellationToken ct);
+    Task<IReadOnlyList<SearchCandidateChunk>> SearchChunksAsync(float[] queryEmbedding, IReadOnlyList<string>? targetTypes, int topK, CancellationToken ct);
+    Task<float[]?> GetEmbeddingAsync(string cacheKey, CancellationToken ct);
+    Task SaveEmbeddingAsync(string cacheKey, string model, string textHash, float[] vector, CancellationToken ct);
+    Task<string?> GetChatCompletionAsync(string cacheKey, CancellationToken ct);
+    Task SaveChatCompletionAsync(string cacheKey, string model, decimal temperature, string responseText, CancellationToken ct);
+}