fix(ux): add client-side validation for empty job search submissions

[Abhi666-max]

📝 Pull Request Description

Related Issue

Closes #391

Summary

Added client-side validation to the JobsForYou component's search form to prevent users from submitting empty or whitespace-only role queries. This blocks unnecessary API requests, conditionally disables the submit button, and displays an inline error message to improve the overall user experience.

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Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature
• ♻️ Refactoring
• 📝 Documentation update
• 🎨 UI/UX improvement
• 🔥 Other(please describe) ______

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How Has This Been Tested?

• Verified that the "Search" button is disabled when the input is empty or contains only whitespace.
• Verified that pressing "Enter" on an empty input prevents form submission and displays the inline "Please enter a role" error message.
• Verified that typing a valid character into the input field immediately clears the error message and re-enables the search button.

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Screenshots (if applicable)

N/A (UI state changes: disabled button and inline error text).

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Checklist

• My code follows the project's guidelines
• I have tested my changes
• I have updated documentation where necessary
• I have linked the related issue
• My changes do not introduce new warnings or errors