Add SEO/meta updates, JSON-LD schema, and sitemap.xml

[joelnishanth]

Motivation

• Improve search engine visibility and social sharing by updating page meta tags and Open Graph/Twitter card data.
• Provide machine-readable site information and product details via structured data to improve indexing and rich results.
• Ensure crawlers see the canonical site and enable basic sitemap discovery for search engines.

Description

• Updated index.html title, meta description, keywords, author, publisher, robots and specific crawler directives for better SEO and privacy hints.
• Reworked Open Graph and Twitter card metadata and switched the preview image to https://apply.offlyn.ai/site/monogram.png for consistent branding.
• Added a script block with application/ld+json JSON-LD containing Organization, WebSite, WebPage, SoftwareApplication, and FAQPage schema to describe the product and site features.
• Added a simple sitemap.xml file that exposes the site root URL for search engines.

Testing

• No automated tests were added or run as part of this change.

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Codex Task