feat(seo): add keywords meta tag support for improved SEO

- Introduced keywords property in layout and page server files to enhance SEO capabilities.
- Updated relevant components to include keywords in meta tags for better search engine visibility.

src/routes/post/[slug]/+page.server.ts

@@ -210,6 +210,7 @@ export const load: PageServerLoad = async ({ params, locals, url }) => {
     seoDescription: postDescription,
     socialImage: postSocialImageAbs ?? postImageUrl ?? undefined,
     robots: (post as { seoMetaRobots?: string }).seoMetaRobots ?? undefined,
+    keywords: (post as { seoKeywords?: string }).seoKeywords ?? undefined,
     jsonLd,
     breadcrumbItems: [
       { href: '/', label: 'Start' },