feat(providers): add Volcengine Ark usage query with AK/SK signing

Query coding-plan / agent-plan usage for Volcengine Ark via the
control-plane OpenAPI (open.volcengineapi.com), which requires
account-level AccessKey signing rather than the inference API key.

- Implement Volcengine Signature V4 (an AWS SigV4 variant: fixed
  canonical header order, "HMAC-SHA256" algorithm without the AWS4
  prefix, scope ending in "request", service "ark") in
  services/coding_plan.rs
- Auto-detect the plan by probing GetAFPUsage (Agent Plan, AFP
  five-hour/weekly/monthly quotas) first, falling back to
  GetCodingPlanUsage (Coding Plan, session/weekly/monthly percentages);
  a single credential covers whichever plan the account holds
- Parse the real response shape: the window label lives in the `Level`
  field; guard ResetTimestamp <= 0 (session returns -1)
- Store account-level credentials on UsageScript (accessKeyId /
  secretAccessKey), threaded through both the test command and the
  TOKEN_PLAN auto-refresh path
- Add an independent AK/SK input block with a detailed hint pointing to
  the Volcengine console -> API Access Keys
- Add the `monthly` tier label (frontend TIER_I18N_KEYS + tray
  TIER_LABEL_GROUPS + subscription service)
- Sync zh / en / ja / zh-TW locales and the usage-query docs

docs/user-manual/ja/2-providers/2.5-usage-query.md

@@ -43,7 +43,7 @@ v3.13.0 では以下のカテゴリに **すぐに使える内蔵テンプレー
 
 | カテゴリ        | 対象プロバイダー                                          | テンプレートタイプ        |
 | --------------- | --------------------------------------------------------- | ------------------------- |
-| Token Plan      | Kimi / Zhipu GLM / MiniMax                                | プランクォータ（使用進捗付き） |
+| Token Plan      | Kimi / Zhipu GLM / MiniMax / Volcengine（火山方舟）       | プランクォータ（使用進捗付き） |
 | 第三者残高      | DeepSeek / StepFun / SiliconFlow / OpenRouter / Novita AI | 公式残高クエリ            |
 
 > **ヒント**：上記の内蔵テンプレート以外で対象外のプロバイダーには、**カスタムスクリプト** 方式（下記参照）で独自のクエリロジックを記述できます。