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/rag-data.csproj

@@ -18,6 +18,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\shared-data\shared-data.csproj" />
+    <ProjectReference Include="..\rag-api-models\rag-api-models.csproj" />
   </ItemGroup>
 
 </Project>