Add warning log for duplicate key violations in SaveMatchAsync

When a match result is inserted concurrently between the existence check and the
database insert, log a warning to help with diagnostics while gracefully handling
the idempotent duplicate key violation.

Apis/cv-matcher-data/Repositories/EfMatcherRepository.cs

@@ -68,6 +68,10 @@ public sealed class EfMatcherRepository : IMatcherRepository
         {
             // Duplicate key violation: record was inserted between the AnyAsync check and SaveChangesAsync.
             // This is safe to ignore — the match result already exists in the database.
+            _logger.LogWarning(
+                "Duplicate match result ignored: CV={CvDocumentId} Job={JobDocumentId} Language={Language}. " +
+                "Record was likely inserted concurrently. This is expected behavior in high-concurrency scenarios.",
+                cvDocumentId, jobDocumentId, language);
         }
     }