feat(carousel): auto-generate homepage carousel from markdown implementation files

Summary

• Adds a Docusaurus plugin that parses Markdown implementation files at build time and auto-generates the homepage carousel data — contributors now only need to edit the Markdown docs
• Replaces the manually-maintained JS pledge files with generated output in .generated/implementations/ (gitignored)
• Fixes broken carousel links that pointed to non-existent /docs/implementations/Certifiers (now correctly points to /docs/implementations/SchemeOwners)
• Picks up 4 previously missing implementations (Health LOQ, SIMBA Chain, K4 Security, Towards Sustainable Mining)

How it works

1. Plugin reads carousel-config.json which maps Markdown files to export names
2. Parses each Markdown file, extracting org name (H3 headings), logo path, and anchor links
3. Filters out placeholder entries (skip markers + missing logos)
4. Generates JS files to .generated/implementations/ before the bundler runs
5. Homepage imports from the generated files

Test plan

• All 41 unit and integration tests pass (node --test plugins/carousel-generator/__tests__/index.test.js)
• docusaurus build succeeds
• Dev server compiles and renders carousel correctly
• Custom anchor IDs (e.g., {#trust-provenance}) handled correctly
• Placeholder entries (Industry "Sample Company") filtered out