Two lines only core cannot supply for itself.
`uo.guild.header` is a third declared slot, at the top of the page, for core's
per-Team notification control. A third rather than a corner of the feed because a
slot holds one component and the first fill wins: the control is an action ON this
page and the other two are content IN it, and separate slots are what let this
module say so.
`pageUrlTemplate` tells core where a guild page actually is. Teams are a contract
primitive with no core surface — core owns the tables and the access rules, this
module owns the word "guild" and therefore the page — which leaves core unable to
write a link to one. A notification email that cannot take you to the thread it is
about is most of the way to useless. Core substitutes `{externalId}` and does
nothing else with it; a template naming its own host is refused at registration.
Co-Authored-By: Claude <noreply@anthropic.com>