Added french configurations for translation and translation for the adoption page

[kayiganwa04]

Added French (fr) localization for the Adoption section and few configuration for language persistance

Summary

• Add full French translation of the Adoption section (Scheme Guide, Hub Operations Guide) under /fr/adoption/
• Configured VuePress with locale-specific navigation, sidebar, and language selector for English (/) and French (/fr/)
• Added a locale-aware 404 page that displays French messages and links when on /fr/ paths
• Implemented automatic language detection in enhanceApp.js that redirects French-speaking browsers to the /fr/ equivalent of the current page on first visit
• Fixed image paths in French files to account for the extra directory depth (docs/fr/adoption/... vs docs/adoption/...)
• Fixed TOC anchor links in 5 translated Scheme documents to match VuePress-generated slugs from French headings

Test plan

• Verify the language dropdown appears and switching between English/Français works
• Navigate through all French Adoption sidebar pages and confirm content renders with images
• Click TOC links on Scheme documents (platform-operating-guideline, scheme-business-rules, etc.) and confirm scrolling works
• Visit /fr/community/ and confirm the French 404 page is shown
• Open the site in a French-language browser and confirm auto-redirect to /fr/
• Confirm English pages remain unaffected