Set DuckLake as default catalog after attaching

After attaching DuckLake, run USE ducklake to set it as the default
catalog. This follows the DuckDB documentation recommendation and
ensures all queries automatically use DuckLake without needing to
prefix table names with ducklake.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: EDsCODE

server/server.go

@@ -327,7 +327,13 @@ func (s *Server) attachDuckLake(db *sql.DB) error {
 		return fmt.Errorf("failed to attach DuckLake: %w", err)
 	}
 
-	log.Printf("Attached DuckLake catalog successfully")
+	// Set DuckLake as the default catalog so all queries use it
+	// See: https://duckdb.org/docs/stable/core_extensions/ducklake#usage
+	if _, err := db.Exec("USE ducklake"); err != nil {
+		return fmt.Errorf("failed to set DuckLake as default catalog: %w", err)
+	}
+
+	log.Printf("Attached DuckLake catalog successfully and set as default")
 	return nil
 }