feat: add frontend source code

Add search-zen-50 React SPA source code to frontend/ directory.
Build artifacts (dist, node_modules, lock files) are gitignored.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/index.css

@@ -0,0 +1,84 @@
+@import url('https://fonts.googleapis.com/css2?family=IBM+Plex+Mono:wght@500;700&family=Inter:wght@400;500;600&display=swap');
+
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+@layer base {
+  :root {
+    --background: 40 33% 97%;
+    --foreground: 220 20% 14%;
+    --card: 40 25% 95%;
+    --card-foreground: 220 20% 14%;
+    --popover: 40 33% 97%;
+    --popover-foreground: 220 20% 14%;
+    --primary: 168 60% 36%;
+    --primary-foreground: 0 0% 100%;
+    --secondary: 40 20% 92%;
+    --secondary-foreground: 220 20% 14%;
+    --muted: 40 15% 90%;
+    --muted-foreground: 220 10% 50%;
+    --accent: 168 60% 36%;
+    --accent-foreground: 0 0% 100%;
+    --destructive: 0 72% 51%;
+    --destructive-foreground: 0 0% 100%;
+    --border: 40 15% 87%;
+    --input: 40 15% 87%;
+    --ring: 168 60% 36%;
+    --radius: 0.5rem;
+    --link: 215 80% 50%;
+    --link-hover: 215 80% 40%;
+    --result-hover: 40 25% 94%;
+    --sidebar-background: 0 0% 98%;
+    --sidebar-foreground: 240 5.3% 26.1%;
+    --sidebar-primary: 240 5.9% 10%;
+    --sidebar-primary-foreground: 0 0% 98%;
+    --sidebar-accent: 240 4.8% 95.9%;
+    --sidebar-accent-foreground: 240 5.9% 10%;
+    --sidebar-border: 220 13% 91%;
+    --sidebar-ring: 217.2 91.2% 59.8%;
+  }
+
+  .dark {
+    --background: 220 20% 8%;
+    --foreground: 40 20% 90%;
+    --card: 220 18% 12%;
+    --card-foreground: 40 20% 90%;
+    --popover: 220 20% 8%;
+    --popover-foreground: 40 20% 90%;
+    --primary: 168 55% 45%;
+    --primary-foreground: 0 0% 100%;
+    --secondary: 220 15% 16%;
+    --secondary-foreground: 40 20% 90%;
+    --muted: 220 15% 18%;
+    --muted-foreground: 220 10% 55%;
+    --accent: 168 55% 45%;
+    --accent-foreground: 0 0% 100%;
+    --destructive: 0 62.8% 30.6%;
+    --destructive-foreground: 0 0% 100%;
+    --border: 220 15% 20%;
+    --input: 220 15% 20%;
+    --ring: 168 55% 45%;
+    --link: 215 75% 62%;
+    --link-hover: 215 75% 72%;
+    --result-hover: 220 18% 14%;
+    --sidebar-background: 240 5.9% 10%;
+    --sidebar-foreground: 240 4.8% 95.9%;
+    --sidebar-primary: 224.3 76.3% 48%;
+    --sidebar-primary-foreground: 0 0% 100%;
+    --sidebar-accent: 240 3.7% 15.9%;
+    --sidebar-accent-foreground: 240 4.8% 95.9%;
+    --sidebar-border: 240 3.7% 15.9%;
+    --sidebar-ring: 217.2 91.2% 59.8%;
+  }
+}
+
+@layer base {
+  * {
+    @apply border-border;
+  }
+  body {
+    @apply bg-background text-foreground antialiased;
+    font-family: 'Inter', system-ui, sans-serif;
+  }
+}