Add SEO structured data and global meta tags

Problem

The Docs site (docs.turbodocx.com) is missing standard SEO configuration that the marketing site already has:

• No JSON-LD structured data (Organization, WebSite schemas)
• No global metadata array in themeConfig (site-wide OG/Twitter defaults)
• No default OG image for pages that don't specify one
• No site-wide description fallback

Individual pages have description and keywords via frontmatter, but there's no structured data or social sharing defaults.

What to add

1. themeConfig.metadata — global meta tags:

   • og:site_name: TurboDocx Documentation
   • og:image: default OG image (1200x630)
   • twitter:card: summary_large_image
   • twitter:site: @turbodocx

2. headTags in config root — JSON-LD scripts:

   • Organization schema (name, url, logo)
   • WebSite schema with SearchAction (for sitelinks search box)

3. Audit all doc pages for description length (150-160 chars target). Several may be too long like the bulk sending page was (249 chars → fixed).

Reference

• Docusaurus SEO docs
• Dotcom site lib/schema.ts for consistent org/rating data

Start with the Docs site's Docusaurus configuration, locating themeConfig and the config-root headTags, then review all documentation pages for description lengths. Use the Docusaurus SEO docs and the listed dotcom schema reference before adding the requested global metadata and JSON-LD schemas. Done means the four defaults, Organization and WebSite SearchAction data, and page descriptions meet the stated targets.