feat(website): move MCP guide into docs

[NicholasKissel]

Stacked on #20.

Summary

• moves the Rivet MCP guide into the shared docs experience at /docs/mcp/
• adds the shared AI Tools group to every product documentation sidebar while preserving each product's docs context
• adds accessible client setup tabs with client logos, copy feedback, and a no-JavaScript fallback
• preserves MCP scope, security, examples, metadata, Markdown exports, footer link, and service routing

Validation

• production build passed on the implementation branch
• SEO and sitemap checks passed
• caddy validate passed
• browser-checked desktop and mobile docs navigation, tabs, copy behavior, and contextual product routes

The isolated stacked-worktree build also passed content sync and route generation; it later hit Astro's shared-node_modules compile-metadata cache-path issue specific to the temporary worktree.

[railway-app]

🚅 Deployed to the website-pr-42 environment in rivet-website

Service	Status	Web	Updated (UTC)
website	😴 Sleeping (View Logs)	Web	Sep 1, 2026 at 9:00 pm