CON-1581: Draft Host Teams page

[jjziets]

Summary

Draft Host Teams page stacked on top of the current vast-ai#153 handover branch.

This PR adds a host-specific Teams page without re-documenting the general Teams guides. It links out to the existing Teams Quickstart, Teams Overview, Teams Roles, Managing Teams, API Keys, and API Permissions pages, then layers on host-specific behavior.

What changed

• Added host/host-teams.mdx
• Added Host nav entry under Host > Operate, after Fleet Operations
• Added cross-links from:
  • host/account-hosting-agreement.mdx
  • host/installing-host-software.mdx
  • host/fleet-operations.mdx
  • host/payment.mdx
  • host/common-host-questions.mdx

Host-specific coverage

The draft covers:

• team context / Context Switcher checks before host operations
• machine ownership in team vs personal context
• installing a host in the correct team context
• machine roles and permissions: machine_read, machine_write
• team API keys for host automation
• team earnings and payout ownership
• recommended setup for a hosting business or multi-operator fleet
• wrong-context troubleshooting, including undefined install command, wrong-account machines, 403 / registration rights, personal-vs-team API keys, and unauthenticated machine errors

Engineering questions before publishing

The draft intentionally uses support-contact wording for these until source-owner behavior is confirmed:

1. Existing individual-host machines -> team: auto-migrate, re-register, or support-only?
2. Existing earnings / payout history -> team: carried over or stays with original account?
3. Current state of the team install-command undefined host-id/API-key issue.
4. Exact flow for granting machine registration rights to team API keys/custom roles.
5. Whether a custom host role can grant billing_read without machine_write.

Validation

• git diff --check -> passed
• authored Host persona coverage -> 36/36 pages have personas: frontmatter and visible chips
• npx --yes mint@4.2.647 validate -> passed
• local preview from moved worktree -> http://localhost:3335/host/host-teams
• route check for /host/host-teams -> 200 OK