Clarify language/timezone handling when nonessential traffic is disabled - #2

When CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC is set, users asked whether Claude can still see device language/timezone.

• Summary of behavior

  • Timezone is only used for local formatting; never sent over the network.
  • System locale language is read only for voice telemetry, which is suppressed under essential-traffic; thus not sent.
  • Voice STT sends only user-configured/default language, not system locale/timezone.

• Docs update

  • Added a “语言与时区” section to USER_DATA_COLLECTION.md, tabulating what’s collected and how CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC gates it.

Example (doc excerpt):

| 项目 | 是否被采集/发送 | 说明与代码位置 |
| 系统时区 | 否 | 仅本地格式化 (`src/utils/intl.ts`, `src/utils/format.ts`) |
| 系统语言 | 遥测事件被禁用时不发送 | 仅语音事件，受 `essential-traffic` 禁用 |
| 语音 STT 语言 | 仅用户设置/默认值 | 不读取系统语言/时区 |