chore(spec): regenerate the email-template reference page over the merged tree

The merge took main's side of the generated page (it carries the header
sentence the registry rename brought); regenerating from the merged sources
puts the two retired-key rows back beside it.

Claude-Session: https://claude.ai/code/session_019G5ZnRrTMiwcHG6iZM19zf
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

content/docs/references/system/email-template.mdx

@@ -13,7 +13,8 @@ to render outbound mail. Read from the metadata registry by
 `(name, locale)` — the environment's item over each code package's
 declaration, the built-in auth templates included — so administrators can
 author/edit/translate templates in Studio without shipping code, and a
-Studio save overrides a built-in default at environment level. No
+Studio save overrides a built-in default at environment level
+(`allowEnvironmentOverlay: true` in the metadata registry). No
 `sys_email_template` row is read or written on the way.
 
 Aligned with Salesforce `EmailTemplate` and ServiceNow