fix(backend): DeepL翻訳のAPIキー指定方式変更に対応 (#16839)

* spec: DeepL Deprecation of query parameter and request body authentication (MisskeyIO#1096)

https://developers.deepl.com/docs/resources/breaking-changes-change-notices/november-2025-deprecation-of-legacy-auth-methods

* Update Changelog

* Update Changelog

* ✌️ [ci skip]

---------

Co-authored-by: あわわわとーにゅ <17376330+u1-liquid@users.noreply.github.com>

packages/backend/src/server/api/endpoints/notes/translate.ts

@@ -95,7 +95,6 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 			if (targetLang.includes('-')) targetLang = targetLang.split('-')[0];
 
 			const params = new URLSearchParams();
-			params.append('auth_key', this.serverSettings.deeplAuthKey);
 			params.append('text', note.text);
 			params.append('target_lang', targetLang);
 
@@ -104,6 +103,7 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 			const res = await this.httpRequestService.send(endpoint, {
 				method: 'POST',
 				headers: {
+					'Authorization': `DeepL-Auth-Key ${this.serverSettings.deeplAuthKey}`,
 					'Content-Type': 'application/x-www-form-urlencoded',
 					Accept: 'application/json, */*',
 				},