Show Best and Mean columns for 3x3x3 Blindfolded results

## Problem

On the competition results page for a 3x3x3 Blindfolded round, both summary columns are labeled `Best` and both render the single result. This is visible on Rubik's WCA European Championship 2026, 3x3x3 Blindfolded Round 1.

The round uses a best-of-3 format, so the current format-only column selection treats both summary columns as `single` even though WCIF/WCA Live also provides the mean in `average`.

## Expected behavior

The summary columns should be shown in this order:

1. `Best`, using `result.best` and the single record tag
2. `Mean`, using `result.average` and the average record tag

## Acceptance criteria

- 3x3x3 Blindfolded result tables render `Best` and `Mean`, not two `Best` columns.
- The two columns display the corresponding best and mean values.
- Record badges remain attached to the correct result type.
- Other event and round-format column behavior remains unchanged.
- Add regression coverage for a 3x3x3 Blindfolded best-of-3 round.

Start at the competition results page's summary-column selection for 3x3x3 Blindfolded and trace how the best-of-3 format maps columns to result fields and record tags. Add regression coverage for this round format, then verify the table shows Best from result.best and Mean from result.average while other event and round-format behavior stays unchanged.

索引モデルが issue の本文から書いたものです。