refactor: use WXT i18n

[jevin98]

Summary

• Replace the Vue i18n dependency with WXT/browser native i18n via browser.i18n.getMessage.
• Move existing English and Chinese translations into public/_locales/*/messages.json.
• Localize extension manifest name and description with __MSG_*__ keys.

Why

WXT already supports browser extension i18n through _locales and the extension i18n API, so the extra vue-i18n dependency is no longer needed.

Impact

• Translation now follows the browser/extension locale instead of an in-panel manual language selector.
• Removes vue-i18n and related lockfile entries while keeping the latest main dependency versions.

Validation

• pnpm install --frozen-lockfile
• pnpm run compile
• pnpm run build:chrome
• Searched for old vue-i18n, $t, $i18n, createI18n, and useI18n references and found none.

[jevin98]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Bravo.

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