Improve mobile responsiveness of the landing page or builder

[sakshisahoo33-arch]

Description:
Problem
The landing page (/) and Resume Builder (/resume-builder) are not fully optimized for mobile screens (widths below 768px). Users on smartphones experience layout issues that hurt usability.

[YAXH64]

@sakshisahoo33-arch I'd like to work on this issue, plz assign it to me under GSSoC'26.

[manjeetsinghmeena]

/assign