feat(reports): add "Overdue" as third category in Reports charts

[ShivaGupta-14]

Description

• Add isOverdue utility function to tasks-utils.ts for shared usage
• Update ReportsView to categorize pending tasks with past due dates as overdue
• Add overdue bar (red #F33434) to ReportChart component
• Update Tasks.tsx to import isOverdue from shared utility
• Add comprehensive test coverage for overdue categorization

Categorization logic:

• status === 'completed' -> Completed (pink)
• status === 'pending' && due < today -> Overdue (red)
• status === 'pending' && (due >= today || no due) -> Ongoing (blue)

Fixes: #341

Checklist

• Ran npx prettier --write . (for formatting)
• Ran gofmt -w . (for Go backend)
• Ran npm test (for JS/TS testing)
• Added unit tests, if applicable
• Verified all tests pass
• Updated documentation, if needed

Additional Notes

Video:

Screen.Recording.2025-12-30.at.1.16.45.AM.mov

[github-actions]

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[ShivaGupta-14]

update the mockData and add test for overdue bar

[ShivaGupta-14]

update test and add new test

[ShivaGupta-14]

add test case for isOverdue

[ShivaGupta-14]

add new overdue bar (red color)

[ShivaGupta-14]

counting overdue task correctly

[ShivaGupta-14]

move isOverdue function to this and make it a shared utility, DRY principle

[ShivaGupta-14]

import isOverdue function from shared utility and removes duplicate code

[ShivaGupta-14]

self review done! ready for review