[Docs] Guide Cloud and self-hosted users through their first task - #3382

What changed

Getting started now gives Roomote Cloud and self-hosting clear entry points, and both lead through a shared guide to a first successful repository task. The self-hosted path puts requirements before installation and explains how one deployment serves multiple computers.

• Add a Cloud setup guide and a first-task walkthrough covering inference, repository access, sandbox execution, and reviewing results. Slack and other communications providers are explicitly optional.
• Nest home-network and hosting-platform guides under self-hosting, with host preparation and networking instructions before install commands.
• Move backup, upgrade, and troubleshooting reference material into an operations guide.
• Align agent installation guidance with the same path, document Docker storage requirements, and replace the Quick Tunnel recommendation because it lacks the event streaming Roomote uses.

How it was tested

• mise exec -- pnpm --filter @roomote/docs check: Mintlify build validation and broken-link checks passed; generated Cookbook content is current.
• Reviewed the rendered local pages and home-network tabs at desktop and narrow widths.
• Pre-push checks passed: oxlint, residual ESLint, check-types:fast, and knip.
• The additional Judgement prose check remained incomplete: inference could not complete, and two pages exceeded its evidence budget. This is not a passing result.