feat: add custom 404 error page

- Create stylish 404 page with glitch animation and CRT scanline effects
- Update nginx to serve custom 404 instead of falling back to index.html
- Page inherits site layout with WebGL background and audio player

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

layouts/404.html

@@ -0,0 +1,147 @@
+{{ define "main" }}
+<style>
+  /* Glitch animation for 404 text */
+  .glitch {
+    position: relative;
+    font-size: clamp(8rem, 20vw, 16rem);
+    font-weight: 700;
+    line-height: 1;
+    color: #fff;
+    letter-spacing: 0.02em;
+    animation: glitch-skew 4s infinite linear alternate-reverse;
+  }
+
+  .glitch::before,
+  .glitch::after {
+    content: attr(data-text);
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+  }
+
+  .glitch::before {
+    color: #ff00ff;
+    animation: glitch-1 2s infinite linear alternate-reverse;
+    clip-path: polygon(0 0, 100% 0, 100% 35%, 0 35%);
+  }
+
+  .glitch::after {
+    color: #00ffff;
+    animation: glitch-2 3s infinite linear alternate-reverse;
+    clip-path: polygon(0 65%, 100% 65%, 100% 100%, 0 100%);
+  }
+
+  @keyframes glitch-1 {
+    0%, 100% { transform: translate(0); }
+    20% { transform: translate(-3px, 3px); }
+    40% { transform: translate(-3px, -3px); }
+    60% { transform: translate(3px, 3px); }
+    80% { transform: translate(3px, -3px); }
+  }
+
+  @keyframes glitch-2 {
+    0%, 100% { transform: translate(0); }
+    20% { transform: translate(3px, -3px); }
+    40% { transform: translate(3px, 3px); }
+    60% { transform: translate(-3px, -3px); }
+    80% { transform: translate(-3px, 3px); }
+  }
+
+  @keyframes glitch-skew {
+    0%, 100% { transform: skew(0deg); }
+    30% { transform: skew(0.5deg); }
+    60% { transform: skew(-0.5deg); }
+  }
+
+  /* Scanline overlay */
+  .scanlines {
+    position: fixed;
+    inset: 0;
+    pointer-events: none;
+    z-index: 10;
+    background: repeating-linear-gradient(
+      0deg,
+      rgba(0, 0, 0, 0.1) 0px,
+      rgba(0, 0, 0, 0.1) 1px,
+      transparent 1px,
+      transparent 2px
+    );
+    animation: scanline-flicker 0.1s infinite;
+  }
+
+  @keyframes scanline-flicker {
+    0%, 100% { opacity: 0.8; }
+    50% { opacity: 0.85; }
+  }
+
+  /* CRT vignette effect */
+  .vignette {
+    position: fixed;
+    inset: 0;
+    pointer-events: none;
+    z-index: 9;
+    background: radial-gradient(
+      ellipse at center,
+      transparent 0%,
+      transparent 60%,
+      rgba(0, 0, 0, 0.4) 100%
+    );
+  }
+
+  /* Button hover effect */
+  .return-btn {
+    position: relative;
+    overflow: hidden;
+    transition: all 0.3s ease;
+  }
+
+  .return-btn::before {
+    content: '';
+    position: absolute;
+    top: 0;
+    left: -100%;
+    width: 100%;
+    height: 100%;
+    background: linear-gradient(
+      90deg,
+      transparent,
+      rgba(255, 255, 255, 0.1),
+      transparent
+    );
+    transition: left 0.5s ease;
+  }
+
+  .return-btn:hover::before {
+    left: 100%;
+  }
+
+  .return-btn:hover {
+    transform: translateY(-2px);
+    box-shadow: 0 0 20px rgba(255, 255, 255, 0.1);
+  }
+</style>
+
+<div class="scanlines"></div>
+<div class="vignette"></div>
+
+<section class="min-h-screen flex flex-col items-center justify-center px-4 relative z-20">
+  <div class="text-center">
+    <h1 class="glitch font-mono" data-text="404">404</h1>
+
+    <p class="mt-8 text-xl md:text-2xl text-text-secondary font-mono tracking-widest uppercase">
+      Signal Lost
+    </p>
+
+    <div class="mt-12">
+      <a
+        href="/"
+        class="return-btn inline-block px-8 py-4 border border-text-secondary/30 text-text-primary font-mono text-sm tracking-wider uppercase hover:border-text-primary/50 focus:outline-none focus:ring-2 focus:ring-text-primary/30 focus:ring-offset-2 focus:ring-offset-bg-primary"
+      >
+        Return Home
+      </a>
+    </div>
+  </div>
+</section>
+{{ end }}