fix: prevent adding empty or whitespace-only tasks to To-Do list (#670)

[harsharajkumar-273]

Description

This PR addresses issue #670 by adding validation checks to prevent users from adding blank tasks or tasks containing only whitespace/spaces to the To-Do list.

Closes #670

Proposed Changes

• Task Title Validation: Implemented .trim() check on form.title inside handleSubmit of Todo.js.
• Form Error State: Introduced local error state in Todo component to capture validation errors and display them directly in the UI.
• Dynamic UX: Automatically clears the error when the user starts typing a valid task title or picks a date.

Verification

• Entering empty strings or spaces only triggers the warning message "Task title is required" and stops submission.
• Form operates normally with valid inputs.

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