feat: add web app i18n skeleton and zh-CN localization

[chinapxe]

Description

Related Issue

Fixes #(issue number)

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Code refactoring
• Test coverage improvement

Changes Made

Testing

Test Plan:

• All existing tests pass (pnpm test)
• TypeScript compiles without errors (pnpm typecheck)
• Added new tests for new functionality
• Manually tested in browser

Browsers Tested:

• Chrome
• Edge
• Other: ___________

Screenshots/Videos

Before:

After:

Checklist

• My code follows the project's coding style (see CONTRIBUTING.md)
• I have performed a self-review of my own code
• I have commented complex/non-obvious code
• I have updated relevant documentation
• My changes generate no new warnings or errors
• I have removed all console.log statements and debug code
• New and existing tests pass locally
• I have checked my code builds successfully

Additional Context

---

Note: This PR will be reviewed by Claude AI within 24 hours. Claude will:

• Run automated checks (TypeScript, tests, linting)
• Provide detailed code review feedback
• Approve or request changes

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[Augani]

Closing — empty PR template, superseded by #28.