feat: add GitHub Pages landing site for the Kibana MCP

[Zacaria]

Summary

• add a one-page GitHub Pages site with a dark landing page, install flows, workflow proof, and support links
• add a Pages deployment workflow and site contract tests to keep the hosted surface aligned with the repo
• realign README.md, INSTALL.md, package metadata, plugin metadata, and project docs with the new homepage and live package story
• refine homepage copy, install commands, and hero interactions, including inline command copy actions

Testing

• npm test -- test/site_contract.test.ts
• npm run check
• npm run verify