feat(seo): upgrade site metadata, schema, and crawl files for OpenFrame rebrand

- update title/description to Open Source Video Review Platform
- add centralized SEO config with canonical URL + meta image (/meta.webp)
- add Open Graph and Twitter card metadata
- add JSON-LD Organization/WebSite structured data
- add robots.txt, sitemap.xml, and web app manifest routes
- version icon metadata to help search engines refresh branding

app/sitemap.ts

@@ -0,0 +1,27 @@
+import type { MetadataRoute } from 'next';
+import { seoConfig } from '@/lib/seo';
+
+export default function sitemap(): MetadataRoute.Sitemap {
+  const lastModified = new Date();
+
+  return [
+    {
+      url: seoConfig.url,
+      lastModified,
+      changeFrequency: 'daily',
+      priority: 1,
+    },
+    {
+      url: `${seoConfig.url}/login`,
+      lastModified,
+      changeFrequency: 'monthly',
+      priority: 0.6,
+    },
+    {
+      url: `${seoConfig.url}/register`,
+      lastModified,
+      changeFrequency: 'monthly',
+      priority: 0.7,
+    },
+  ];
+}