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/email-api-data/Migrations/20260528130652_SeedEmailTemplates.cs

@@ -1,4 +1,5 @@
 using Microsoft.EntityFrameworkCore.Migrations;
+using EmailApi.Data;
 
 #nullable disable
 
@@ -31,7 +32,7 @@ namespace EmailApi.Data.Migrations
                 => m.InsertData("EmailTemplates",
                     ["Key", "Language", "Value", "Description", "OperatorCopy"],
                     [key, lang, value, description, operatorCopy],
-                    "emailApi");
+                    MigrationConstants.SchemaName);
 
             // ── HTML shell (no operator copy — these are layout fragments, not addressable emails) ──
             Row("email.html-shell.start", "*",