Fix language files that break Spanish, Welsh and Uzbek locales

[theluckystrike]

Three locale files break when Laravel loads them.

What users see:

• Spanish: lang/es/validation.php lines 1 to 3 hold leftover text from a translation tool ("Aquí está la traducción al español:" and a ```php fence) before the opening <?php tag. Laravel requires the file to load the validation group, so that text is printed into the page output whenever a Spanish validation message is used.
• Welsh: lang/cy/auth.php:24 has an unescaped apostrophe in Dyma'r. The file doesn't parse, so any trans('auth.*') call for a cy user or app throws a ParseError (for example the wrong password message on the password protection page).
• Uzbek: lang/uz_Latn/auth.php:19 (Yorug') and :24 (noto'g'ri) have the same problem.

Changes:

• Remove the 3 stray lines from es/validation.php.
• Escape the apostrophes in cy/auth.php and uz_Latn/auth.php. The translated strings stay the same.
• Add tests/Feature/LanguageFilesTest.php. It requires every lang//.php file and checks that it returns an array and prints nothing.

Verification:

• php -l on main: lang/cy/auth.php and lang/uz_Latn/auth.php fail with "syntax error". On this branch all 641 lang//.php files pass.

• Loading es/validation.php on main prints the 48 bytes of leftover text. On this branch it prints nothing and returns 78 keys.

• The new test: 3 failures against the lang files from main (cy/auth, uz_Latn/auth, es/validation), 641 passed on this branch.

• Full Pest suite locally: the same 107 tests fail on main and on this branch. My setup has no frontend build (no Vite manifest). No new failures.