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

lib/seo.ts

@@ -0,0 +1,45 @@
+const FALLBACK_SITE_URL = 'https://openframe.net';
+
+function normalizeSiteUrl(rawUrl: string | undefined): string {
+  if (!rawUrl) {
+    return FALLBACK_SITE_URL;
+  }
+
+  const trimmed = rawUrl.trim();
+
+  if (!trimmed) {
+    return FALLBACK_SITE_URL;
+  }
+
+  const withProtocol = /^https?:\/\//i.test(trimmed) ? trimmed : `https://${trimmed}`;
+
+  try {
+    return new URL(withProtocol).origin;
+  } catch {
+    return FALLBACK_SITE_URL;
+  }
+}
+
+export function getSiteUrl(): string {
+  return normalizeSiteUrl(process.env.NEXT_PUBLIC_APP_URL ?? process.env.NEXTAUTH_URL);
+}
+
+export const seoConfig = {
+  name: 'OpenFrame',
+  title: 'Open Source Video Review Platform',
+  description:
+    'OpenFrame is an open source video review platform for collecting timestamped feedback with text and voice comments.',
+  keywords: [
+    'open source video review platform',
+    'video review tool',
+    'timestamped video feedback',
+    'video collaboration',
+    'video annotation',
+    'creative review workflow',
+  ],
+  url: getSiteUrl(),
+  ogImage: '/meta.webp',
+  logoPath: '/icon.svg',
+  logo: '/icon.svg?v=2',
+  githubUrl: 'https://github.com/yusufipk/OpenFrame',
+} as const;