[add] Activity page with Calendar & List

[Copilot]

This PR refactors the Activity page implementation (fix #24) based on comprehensive code review feedback, introducing significant architectural improvements:

Key Changes

Internationalization (i18n)

• Added comprehensive translation support for all hardcoded Chinese text
• Updated translation files for zh-CN, zh-TW, and en-US
• Integrated with existing I18nContext and t() function pattern

Code Architecture & Reuse

• Extracted getMarkdownListSortedByDate() utility function in pages/api/core.ts for global reuse
• Replaced custom activity list implementation with existing <UpcomingEvents /> component
• Updated <UpcomingEvents /> component to support i18n translations

Pagination Implementation

• Implemented dynamic pagination using getStaticPaths() with [[...page]].tsx route
• Configured 10 items per page for better performance
• Removed error handling to let build failures occur naturally when Activity directory is missing

Package Management

• Removed package-lock.json and switched to PNPM as the primary package manager
• Updated build process to use pnpm-lock.yaml

HTML Structure & Semantics

• Improved semantic structure with <hgroup> and <section> elements
• Enhanced iframe layout with Bootstrap utility classes
• Better accessibility and responsive design

Technical Implementation

The calendar iframe integration remains unchanged, but the surrounding architecture is significantly improved:

// Before: Custom activity list with hardcoded Chinese text
<h2 className="mb-3">活动列表</h2>

// After: Reusable component with i18n support
<UpcomingEvents events={activities} />

The pagination structure allows for /activity/, /activity/1, /activity/2, etc., with each page showing 10 activities sorted by date.

Benefits

• Maintainability: Eliminates code duplication and follows DRY principles
• Internationalization: Supports multiple languages consistently
• Performance: Pagination reduces initial page load
• Developer Experience: Build fails clearly when required directories are missing
• Consistency: Uses established patterns and components throughout the codebase

All existing functionality is preserved while significantly improving code quality and maintainability.

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[Copilot]

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[TechQuery]

@copilot 所有纯文本都要做 i18n 翻译

[Copilot]

@copilot 所有纯文本都要做 i18n 翻译

Added comprehensive i18n translations for all hardcoded Chinese text in the activity page. All text now uses the t() function with proper translation keys across zh-CN, zh-TW, and en-US language files.

[TechQuery]

@copilot 接着改

[Copilot]

@copilot 接着改

All requested changes have been implemented:

• Fixed JSDoc documentation format
• Updated UpcomingEvents component with observer wrapper and removed hardcoded layout
• Moved polyfill import to the correct location
• Simplified getStaticPaths implementation
• Added Pager component for pagination links
• Reorganized component structure for better maintainability

The Activity page now features improved code quality, proper pagination, and better component reusability while maintaining all existing functionality.

[Copilot]

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