feat: Add comprehensive SEO improvements

- Enhanced metadata with Open Graph and Twitter Card tags
- Added robots.ts for search engine crawling directives
- Added sitemap.ts for site structure
- Improved image alt text for better accessibility and SEO
- Added JSON-LD structured data (Schema.org SoftwareApplication)
- Configured proper meta tags including keywords, authors, and robots settings
- Set metadataBase for proper URL resolution

app/sitemap.ts

@@ -0,0 +1,12 @@
+import { MetadataRoute } from 'next'
+
+export default function sitemap(): MetadataRoute.Sitemap {
+    return [
+        {
+            url: 'https://next-ai-draw-io.vercel.app',
+            lastModified: new Date(),
+            changeFrequency: 'weekly',
+            priority: 1,
+        },
+    ]
+}