fix(BlogList): support arbitrary locale for date formatting

[dragomano]

Problem

The BlogList component accepts a lang prop, but date formatting ignores it. The locale is hardcoded to either zh-CN or en-US, so any other language (Russian, German, Japanese, etc.) always renders dates in English format regardless of the lang value passed.

Root cause

In BlogList, the Intl.DateTimeFormat instance is created with a hardcoded locale:

const dateFormatter = new Intl.DateTimeFormat('zh' === lang ? 'zh-CN' : 'en-US', dateFormatOptions);

Fix

Pass lang directly to Intl.DateTimeFormat, keeping the zh → zh-CN normalization and falling back to en-US only when lang is not provided:

const dateFormatter = new Intl.DateTimeFormat(lang === 'zh' ? 'zh-CN' : lang || 'en-US', dateFormatOptions);

Why this is safe

Intl.DateTimeFormat accepts any valid BCP 47 language tag. If an unsupported tag is passed, it falls back gracefully. Existing behavior for zh and en is unchanged.

Fixes #95