feat: sort Chinese app labels by pinyin

[AstronW]

Type of Change

• Feature

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Pre-Submission Checklist

• No existing Pull Request for this change
• Descriptive commit message
• Self-reviewed the code
• Comments added where necessary
• No new warnings or errors introduced
• Changes made in a separate branch
• Branch named using prefix (e.g., bug/, feat/, clean/, release/)
• All user-facing text supports localization (if applicable)
• Updated documentation or relevant README sections (if applicable)
• Added screenshots or demo for UI changes (if applicable)

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Before Submitting Your Pull Request

• Clear and descriptive PR title
• Detailed summary of the changes made
• Linked relevant issue(s) using Closes #XXXX or Fixes #XXXX (if applicable)

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Summary of Changes

Adds pinyin-based sorting and section indexing for Chinese app labels only when the launcher language is Chinese, or when it follows a Chinese system language.

Key Changes

1. Added ChineseSortHelper to centralize Chinese-specific sorting behavior.

   • Chinese sorting is only enabled when the app language is set to Chinese, or when the app follows the system language and the system language is Chinese.
   • Other app language settings keep the existing sorting behavior unchanged.
   • The helper returns null outside this narrow Chinese-language scope, so callers naturally fall back to the original label-based sorting.

2. Updated app list sorting to use pinyin keys only in Chinese-language contexts.

   • MainViewModel.normalizeForSort() asks ChineseSortHelper.sortKey(...) for a pinyin sort key.
   • A pinyin key is only produced for Chinese-leading labels in a Chinese-language context.
   • Non-Chinese language contexts and non-Chinese-leading labels continue through the existing normalization path.

3. Updated App Drawer section indexing to use pinyin initials only in Chinese-language contexts.

   • App list scroll mapping and the A-Z sidebar ask ChineseSortHelper.sectionKey(...) for a pinyin initial.
   • Chinese app names can appear under their pinyin initials, such as 微信 under W.
   • Pinned apps still use the existing ★ section, and all labels outside the Chinese-language scope keep the previous first-character section behavior.

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Test Information

• MultiLauncher Version: b947f47
• Device Name: Android Emulator
• Android Version: Android 17 and Android 9 / API 28
• Other Notes: Android 17 uses pinyin sorting correctly for Chinese app names. Android 9 / API 28 falls back to the existing sorting behavior correctly because ICU transliteration is only used on API 29+.