Render DNF and DNS instead of raw negative result sentinels

## Problem

Competition result values use WCA sentinel values for non-results:

- `-1` means `DNF`
- `-2` means `DNS`

The current result formatter passes these values through numeric event formatting, so result tables can display the raw values `-1` and `-2`. This is visible in the Lipnica Wielka Open 2026 results screenshot.

## Expected behavior

Every displayed attempt, best, average, or mean result should render the WCA status text instead of the sentinel number:

- `-1` -> `DNF`
- `-2` -> `DNS`

## Acceptance criteria

- Negative WCA result sentinels are handled before event-specific formatting.
- `-1` renders as `DNF`.
- `-2` renders as `DNS`.
- Normal centisecond, FMC, and Multi-Blind result formatting remains unchanged.
- Existing zero-value placeholder behavior remains unchanged.
- Add focused regression tests for both sentinels.

Locate the result formatter used by the competition result tables and inspect where values enter event-specific formatting. Add focused regression coverage for -1 and -2, verifying DNF and DNS while preserving normal centisecond, FMC, Multi-Blind, and zero-value placeholder behavior.

Written by the indexing model from the issue text.