feat: add Contact Us page with form and footer link

[ArshiBansal]

Description

Added a new Contact Us page and integrated it into the footer for better user accessibility.

Changes:

• Created src/app/contactus/page.tsx with a modern, responsive contact form
• Added dropdown selection for Subject with relevant options
• Added success state, error handling, loading state, and form validation
• Added Mail icon and "Contact Us" link in the Links section of the footer (src/components/layout/footer.tsx)
• Used consistent styling with the rest of the application

This improves user experience by providing a dedicated, professional way for users to reach out to the team.

Fixes #627

Type of change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Local testing
• Vercel Preview Deployment

Test Steps:

• Navigated to /contactus page
• Verified form validation (required fields)
• Submitted form and checked success state
• Verified footer link works correctly
• Checked responsiveness on mobile and desktop

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings or errors
• I have checked that the "DevPath India" branding remains intact