style(sections): double vertical spacing and bump section headings 10%

[opensesh]

Summary

• Doubled vertical spacing between Hero, Free Resources, Recent Blogs, and Our Tools across mobile/tablet/desktop
• Increased section h2 size by ~10% (text-xl 20px → text-[1.375rem] 22px) for Free Resources, Recent Blogs, Our Tools
• Hero left untouched — first section, not a between-sections gap

Test plan

• Visual check on desktop (>=1024px), tablet (768–1023px), mobile (<768px)
• Confirm section headings read slightly larger but still feel balanced

🤖 Generated with Claude Code