feat(i18n): bring the Azerbaijani translation up to date with dev

Translates the keys dev gained since the branch was cut, the help center
above all, and drops the six keys dev no longer has. Registers az
everywhere a language is listed: notification emails, the rate-limit
message, the placeholder check and the wiki. The two tests that counted
the languages by hand now derive the count from SUPPORTED_LANGUAGES.

client/src/api/client.ts

@@ -124,6 +124,7 @@ const RATE_LIMIT_MESSAGES: Record<string, string> = {
   it:      'Troppi tentativi. Riprova più tardi.',
   tr:      'Çok fazla deneme. Lütfen daha sonra tekrar deneyin.',
   ar:      'محاولات كثيرة جدًا. يرجى المحاولة لاحقًا.',
+  az:      'Həddindən çox cəhd edildi. Bir az sonra yenidən cəhd edin.',
   id:      'Terlalu banyak percobaan. Coba lagi nanti.',
   ja:      '試行回数が多すぎます。時間をおいて再度お試しください。',
   ko:      '시도 횟수가 너무 많습니다. 잠시 후 다시 시도해 주세요.',