feat(AddTaskDialog): add end date datetime picker

[ShivaGupta-14]

Description

• Replace DatePicker with DateTimePicker for end field in AddTaskDialog

• Add end to dateTimeFields array in tests

• Support both date-only and datetime formats for end

• Mark task as completed when end date is set via task done command in backend

• Show inline warning message when end date is selected

• Add warning message visibility tests

• Fixes: Add additional time picker for time(and date) based fields in AddTaskDialog #325

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

Why task done is used: Taskwarrior does not allow setting an end date on a pending task. The only way is via task done end:<date>, which marks the task as completed. Future end dates are allowed (as discussed with maintainer), the inline warning informs users of completion behavior.

Screenshots:

Video:

Screen.Recording.2026-01-19.at.12.34.40.AM.mov

[github-actions]

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[ShivaGupta-14]

removed end from cmdArgs (not allowed on pending tasks). Using task done end:<date> to set end date and mark task completed, the way in Taskwarrior.

[ShivaGupta-14]

update the tests and added test for warning message

[ShivaGupta-14]

self review done, ready for review, open to feedback and suggestions