Split files into CSS/JS/HTML + add mobile menu

- Extracted CSS to css/style.css (978 lines)
- Extracted JS to js/main.js (708 lines)
- index.html now only 608 lines (was 2289)
- Added mobile hamburger menu for navigation
- Mobile menu toggles with animated icon
- Menu closes when clicking links or outside

partials/hero.html

@@ -0,0 +1,10 @@
+    <!-- Hero - Laevatain -->
+    <section class="hero" id="hero">
+        <img src="characters/Laevatain_Splash.png" alt="Laevatain" class="hero-character">
+        <div class="hero-content">
+            <div class="hero-badge">SS TIER // HEAT ELEMENT</div>
+            <h1><span class="outline">LAEVATAIN</span></h1>
+            <p>"Twilight of ruin!" - Best DPS in Arknights Endfield. Triggers Arts Bursts constantly for devastating damage.</p>
+            <div class="scroll-indicator">↓</div>
+        </div>
+    </section>