feat(hackathon): update landing page and auth page UI (#60)

* feat: update landing page

* feat: Add favicon and SEO (JSON-LD schema, meta tags)

- Add favicon image
- Add JSON-LD schema for Hackathon event
- Add react-helmet-async for managing meta tags

* chore: remove react-helmet-async

* chore: update landing page

* chore: update UI for signup and login

- add back button for better UX

---------

Co-authored-by: Maulana Sodiqin <sodiqincahyana1@gmail.com>

apps/hackathon/index.html

@@ -4,7 +4,6 @@
     <meta charset="utf-8" />
     <title>IMPHNEN x Kolosal.ai Hackathon 2025</title>
     <base href="/" />
-
     <meta name="viewport" content="width=device-width, initial-scale=1" />
     <meta
       name="description"
@@ -20,7 +19,6 @@
       href="/images/imphnen-logo-simple.svg"
     />
     <link rel="stylesheet" href="/src/index.css" />
-    <!-- Open Graph -->
     <meta property="og:type" content="website" />
     <meta property="og:url" content="https://hackathon.imphnen.dev/" />
     <meta property="og:title" content="IMPHNEN x Kolosal.ai Hackathon 2025" />
@@ -28,7 +26,6 @@
       property="og:description"
       content="Total hadiah Rp14.500.000! Daftar sekarang dan wujudkan inovasi AI-mu untuk membantu usaha lokal."
     />
-
     <meta property="twitter:card" content="summary_large_image" />
     <meta property="twitter:url" content="https://hackathon.imphnen.dev/" />
     <meta