Refactor datetime handling to use dayjs consistently and centralize format constants

[Copilot]

• Refactor utils/learning-center/date.ts to use dayjs
• Refactor utils/learning-center/history-appointment-status.ts to use dayjs
• Refactor components/course/course-week.tsx to use dayjs
• Refactor components/course/time-col.tsx to use dayjs
• Refactor lib/course.ts toLocaleString() calls to use dayjs
• Refactor lib/locate-date.ts to use dayjs
• Refactor app/(guest)/index.tsx toDateString() to use dayjs
• Refactor app/toolbox/exam-room.tsx to use dayjs
• Refactor app/toolbox/learning-center/time-select.tsx to use dayjs
• Refactor app/toolbox/learning-center/qr-scanner.tsx to use dayjs
• Refactor app/toolbox/academic/unified-exam.tsx to use dayjs
• Refactor app/toolbox/academic/grades.tsx to use dayjs
• Refactor app/toolbox/academic/credits.tsx to use dayjs
• Refactor app/common/about.tsx to use dayjs
• Refactor app/common/academic-calendar.tsx to use dayjs
• Refactor app/devtools/learning-center-api.tsx to use dayjs
• Refactor app/toolbox/learning-center/seat-time-status.tsx to use format constants
• Address code review feedback
• Use DATETIME_SECOND_FORMAT constant instead of hardcoded strings
• Add DATE_FORMAT_DASH constant for 'YYYY-MM-DD' format
• Replace all hardcoded format strings with constants from lib/constants.ts
• Lint and verify all changes

All datetime handling code has been successfully refactored to use dayjs library instead of native JavaScript Date methods. All datetime format strings are now centralized in lib/constants.ts for consistency and maintainability.

Code Review Feedback Addressed:

• Fixed remaining new Date() call in utils/learning-center/date.ts
• Simplified QR scanner time validation using isSameOrAfter and isSameOrBefore plugins
• Replaced hardcoded format strings with DATETIME_SECOND_FORMAT constant from lib/constants
• Added new DATE_FORMAT_DASH constant for 'YYYY-MM-DD' format
• Replaced all hardcoded 'YYYY-MM-DD' with DATE_FORMAT_DASH
• Replaced all hardcoded 'HH:mm' with TIME_FORMAT

Impact:

• All datetime formats are now centralized in lib/constants.ts
• Improved code maintainability by eliminating hardcoded format strings
• Consistent datetime handling across the entire codebase
• All changes pass linting with no new warnings introduced

Original prompt

Refactor existing codes about datetime display which is not handled by dayjs. For usage of dayjs, please reference current codebase with dayjs.

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[renbaoshuo]

cc @Seeridia @weijianxian (original author) to review learning-center-related code

[klxiaoniu]

@copilot 涉及到日期时间格式的，使用我们先前在constants.ts中的定义，如果没有定义的话就添加对应定义并在代码中引用

[Copilot]

@copilot 涉及到日期时间格式的，使用我们先前在constants.ts中的定义，如果没有定义的话就添加对应定义并在代码中引用

Fixed in 2cedc25. Added DATE_FORMAT_DASH constant to lib/constants.ts and replaced all hardcoded format strings:

• 'YYYY-MM-DD' → DATE_FORMAT_DASH
• 'HH:mm' → TIME_FORMAT

All datetime format strings now use constants from lib/constants.ts.