[Repo Assist] fix: align configSearch file priority with PHP_CodeSniffer's auto-detection order

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🤖 This is an automated draft PR from Repo Assist.

Problem

The confFileNames array in getStandard() had its entries in the wrong order relative to what PHP_CodeSniffer itself uses when auto-detecting ruleset files.

Extension's previous order:

.phpcs.xml → .phpcs.xml.dist → phpcs.xml → phpcs.xml.dist → phpcs.ruleset.xml → ruleset.xml
```

**PHP_CodeSniffer's actual order** (from [`Config.php`](https://github.com/PHPCSStandards/PHP_CodeSniffer/blob/master/src/Config.php)):
```
.phpcs.xml → phpcs.xml → .phpcs.xml.dist → phpcs.xml.dist

The bug: .phpcs.xml.dist was placed before phpcs.xml. This means if a project had both .phpcs.xml.dist (a distribution template) and phpcs.xml (the actual project config) in the same directory, the extension would pass .phpcs.xml.dist to --standard= instead of phpcs.xml.

Fix

Reorder confFileNames to match PHPCS's own priority:

['.phpcs.xml', 'phpcs.xml', '.phpcs.xml.dist', 'phpcs.xml.dist', 'phpcs.ruleset.xml', 'ruleset.xml']
```

The two PHPCS-style legacy names (`phpcs.ruleset.xml`, `ruleset.xml`) remain at the end since PHPCS no longer includes them in its own discovery but older projects may still use them.

## Test Status

Three new priority-ordering unit tests added to `test/unit.test.js`:

```
✔ findFiles (10/10 passing) ✅
  including:
  ✔ PHPCS priority: .phpcs.xml beats phpcs.xml when both exist
  ✔ PHPCS priority: phpcs.xml beats .phpcs.xml.dist when both exist
  ✔ PHPCS priority: .phpcs.xml.dist beats phpcs.xml.dist when both exist

node --check extension.js: OK ✅

No CI workflow exists in this repository; all checks are manual.

Impact

This is an edge-case fix — it only affects users who have multiple config files in the same directory (e.g. a project with both .phpcs.xml.dist checked in as a template and phpcs.xml as the active config). For everyone else, the behaviour is unchanged.

Relates to #17 (extension ignores phpcs.xml).

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