Modernize Apache Unomi website: Bootstrap 5, design system, AI positi… (#40)

Modernize Apache Unomi website: Bootstrap 5, design system, AI positioning, SEO/AEO

Complete redesign of the Apache Unomi website including:

Infrastructure:
- Upgrade Bootstrap 4 to 5.3.8 and Jekyll 4.2.0 to 4.4.1
- Add Mermaid.js v11 for interactive diagrams
- Centralized CSS design system with 40+ CSS custom properties
- Docker-based build workflow using bretfisher/jekyll images

Content & Pages:
- New "CDP in the AI Era" section and AI-first positioning throughout
- New Integrations page with randomized company order (ASF compliance)
- Rewritten Tutorial page for Unomi 3.0
- Rebuilt Events page with 12 talks, local video thumbnails
- Testing guide TODOs filled in from source code research
- Dependencies guide: added BOM documentation for Unomi 3
- Latest News timeline combining releases, articles, and events (capped at 10)
- Use cases reordered with AI & ML first

Community & Design:
- Team page redesigned as responsive card grid with updated affiliations
- All 11 contribute sub-pages modernized (layout only, text preserved)
- Fixed empty mailing list cards, encoding issues, dead links
- Copyright years updated to 2026

SEO & AI Engine Optimization:
- JSON-LD structured data (Schema.org) on all pages
- Open Graph and Twitter Card meta tags
- robots.txt, sitemap.xml, llms.txt, llms-full.txt added

Staging preview: https://unomi-v3-site.netlify.app/

* CSS design system: centralized variables, utility classes, DRY cleanup

- Add new CSS variables for rgba variants, opacity levels, and color tokens
- Create 10+ utility classes to replace inline styles (badges, icons, overlays)
- Merge duplicate CSS rules (.mermaid, media queries, button hovers)
- Add vendor prefix (-webkit-backdrop-filter) for Safari
- Fix color contrast for WCAG AA compliance (hero text opacity)
- Add mobile overflow protection for Mermaid diagrams and code blocks
- Extract shared Fisher-Yates shuffle script to assets/js/shuffle.js

* Layout: performance, accessibility, SEO and navigation improvements

- Conditional Mermaid.js loading (saves ~25KB on pages without diagrams)
- Defer Bootstrap JS and Mermaid scripts for faster initial render
- Preconnect to cdn.jsdelivr.net, non-blocking Bootstrap Icons CSS
- Add :focus-visible styles for keyboard navigation accessibility
- Replace footer <h6> with role="heading" for semantic hierarchy
- Shorten <title> suffix to keep under 65 characters
- Normalize og:url to match canonical URL
- Update navbar Slack link to point to access instructions
- Update navbar mailing list link to point to community page
- Update JSON-LD featureList (Salesforce deprecated, Groovy actions)
- Fix broken links to generated docs with absolute URLs

* Content pages: AI positioning, ES 9.1.3, structured data, inline style cleanup

- Homepage: fix traveling data dots animation, AI era section, OpenSearch wording
- Use cases: reorder AI use case first, center graphs, add FAQPage schema
- Tutorial & get-started: update to Elasticsearch 9.1.3 with xpack.security
- Documentation: add CollectionPage schema, fix heading hierarchy, absolute links
- Resources: add CollectionPage schema, new video entries, local thumbnails
- Download: fix broken link to quick start guide
- All pages: replace inline styles with CSS classes, add SEO keywords
- Correct "ElasticSearch" trademark spelling across all pages

* Community, events, integrations: Slack access, Salesforce removal, ASF compliance

- Community: rewrite Slack card with ASF access paths, update monthly meeting
  with direct Zoom link and 'open to all' messaging, add mailing list anchor
- Team: modernize to card layout, update affiliations, lazy-load gravatars
- Events: restructure past events with local thumbnails, add CollectionPage schema
- Integrations: remove Salesforce connector, add Groovy actions (recommended)
  and Java plugins guidance, remove Unomi UI/Inoyu UI cards for ASF compliance,
  use generic labels in Mermaid diagram
- Connectors: update description for Salesforce deprecation
- Stories: replace inline shuffle script with shared shuffle.js
- All pages: fix rel="noopener", protocol upgrades, inline style cleanup

* Contribute pages, SEO & LLM files: testing TODOs, release guide, sitemap

- Testing: replace TODOs with Surefire/Failsafe/Pax Exam docs, add CI section
- Dependencies: add BOM section with usage examples
- Release guide: update versions to 3.0.x, fix typos and stale URLs
- Manual release guide: update version examples, fix typos
- Encoding fixes: correct mojibake characters on 3 contribute pages
- Sitemap: expand from 14 to 29 URLs, add lastmod dates
- Robots.txt: remove CSS/JS disallow rules for proper Google rendering
- LLM files: update to 3.0.0, Groovy/Java plugin guidance, OpenSearch wording,
  Salesforce deprecation, Slack access, remove excess Inoyu product listings
- All contribute pages: add SEO keywords, fix rel="noopener"