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

src/types.ts

@@ -62,6 +62,8 @@ export interface UsageScript {
   baseUrl?: string; // 用量查询专用的 Base URL（通用和 NewAPI 模板使用）
   accessToken?: string; // 访问令牌（NewAPI 模板使用）
   userId?: string; // 用户ID（NewAPI 模板使用）
+  accessKeyId?: string; // 火山方舟 AccessKey ID（用量查询签名用，与推理 Key 分离）
+  secretAccessKey?: string; // 火山方舟 SecretAccessKey
   codingPlanProvider?: string; // Coding Plan 供应商标识（如 "kimi", "zhipu", "minimax"）
   autoQueryInterval?: number; // 自动查询间隔（单位：分钟，0 表示禁用）
   autoIntervalMinutes?: number; // 自动查询间隔（分钟）- 别名字段