feat: add mobile bottom navigation bar

[MsParadox]

📱 Feature: Mobile Bottom Navigation Bar

Closes #101

📝 Description

Implemented a native-style Bottom Navigation Bar to improve mobile UX. The top navbar on mobile often requires opening a hamburger menu to navigate, slowing down power users. This new bottom tab bar places the 5 core routes at the user's fingertips.

🛠️ Changes Made

• Created BottomNav.tsx: Built a fixed, glass-morphism bottom bar containing Leaderboard, Models, Feed, Contribute, and Search tabs.
• Dynamic Active States: Integrated Next.js usePathname to accurately highlight the active tab using atlas-blue.
• Integrated Safe Area Inset: Used env(safe-area-inset-bottom) to ensure it doesn't collide with the iOS home indicator bar.
• Updated globals.css: Added dynamic padding to the <main> tag strictly for screens < 768px to prevent content overlapping.
• Updated layout.tsx: Mounted the component globally so it persists seamlessly across page transitions.

✅ Acceptance Criteria Completed

• Visible on mobile only (< 768px).
• All 5 tabs functional.
• Active state correct on all routes.
• Doesn't overlap page content.
• Works correctly alongside the top navbar.

[vercel]

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[AditthyaSS]

@MsParadox plz resolve conflicts asap