Update docs for 21 command types, add web manifest and structured data

[MelbourneDeveloper]

TLDR;

Website and documentation updates: bump command count from 19 to 21 (C# Script, F# Script), add web manifest, twitter image alt tags, SoftwareApplication structured data, and remove stale CoveragePlan.md.

Details

• Updated all references from "19 command types" to "21 command types" across README, website homepage, docs, and blog
• Added C# Script (.csx) and F# Script (.fsx) entries to all command type listings
• Added site.webmanifest with PWA-style metadata and favicon references
• Added twitter:image:alt meta tag injection in eleventy config
• Added SoftwareApplication JSON-LD structured data schema to homepage
• Updated favicon.ico
• Deleted CoveragePlan.md (stale planning artifact)
• Added social media preview cards reference to CLAUDE.md

How do the tests prove the change works

Homepage Playwright test updated to assert 21 command types (was 19) and verify C# Scripts and F# Scripts appear in the expected types list.