docs: add subdomain routing to preview environments documentation

[roomote]

Documents the subdomain field added to named port configuration in RooCodeInc/Roo-Code-Cloud#2391.

Changes

• Added subdomain to the Port Configuration Fields table
• Added a new "Subdomain Routing" subsection explaining how the feature works, validation rules, and use cases
• Added "Subdomain Routing" to frontmatter keywords

The subdomain field enables frameworks that use subdomain-based routing (Rails, Django, Phoenix) to work in sandbox environments by rewriting the Host header to {subdomain}.localhost:{port} inside the proxy.

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View task on Roo Code Cloud

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Important

Adds documentation for subdomain field in port configuration, enabling subdomain-based routing in preview environments.

• Documentation:
  • Adds subdomain field to Port Configuration Fields table in environments.mdx.
  • Introduces "Subdomain Routing" subsection explaining feature, validation rules, and use cases.
  • Adds "Subdomain Routing" to frontmatter keywords.
• Functionality:
  • subdomain field rewrites Host header to {subdomain}.localhost:{port} for subdomain-based routing in sandbox environments.
  • Supports frameworks like Rails, Django, and Phoenix.

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Project	Deployment	Actions	Updated (UTC)
roo-code-docs	Ready	Preview, Comment	Feb 9, 2026 0:46am

[roomote]

Rooviewer   See task

All previously flagged issues have been resolved. No new issues found.

• DNS label vs DNS hostname: The validation rules section incorrectly describes the value as a "DNS label" when dots are allowed and the max length is 253 characters (both properties of a DNS name/hostname, not a label).

Previous reviews

• af2ae30: Review #1

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}

[roomote]

Rooviewer   See task

All previously flagged issues have been resolved. No new issues found.

• DNS label vs DNS hostname: The validation rules section incorrectly described the value as a "DNS label" when dots are allowed and the max length is 253 characters. Fixed in 579601c.

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}