fix(kit): what installing the template into a real core showed

The template was built into a running core - MariaDB, the real loader, a browser
- and both halves of the walk passed: core reconciled two Teams out of the
provider on the first boot, /public/teams/<slug>/members came back with
projected:true, and the clan page rendered core's activity feed and forum in the
two slots this module declared. That last one is the whole point of the phase: a
module whose id is not "uo" now gets core's Team content, which is what
website#160 fixed. module-uo's own guild page was walked on the same core and is
unchanged.

Two things the walk found, both of the kind only a browser can:

PageHeader takes `lead`, not `subtitle`. The template has been passing subtitle
since it was written, and an unknown prop on a React component is silently
dropped - so every page built from this template rendered its heading with
nothing under it, on a site where every core page has a line there. Nothing warns
anywhere. Fixed on all three pages, and chapter 2 now says to check prop names
against 3.4 rather than guessing them, beside the paragraph about `shell` that
exists for exactly the same reason.

"1 members" on the clan list.

Co-Authored-By: Claude <noreply@anthropic.com>

book/02-website-module.md

@@ -566,6 +566,14 @@ That paragraph exists because the kit's acceptance run
 ([`kit-acceptance.md`][acceptance]) built a module by following this chapter to the
 letter, and its page rendered outside the site. Everything else it wrote was right.
 
+**And check a component's prop names against [§3.4][api] rather than guessing
+them.** `PageHeader` takes `eyebrow`, `title`, `lead` and `center` — a page that
+passes `subtitle` renders its heading and nothing under it, because an unknown
+prop on a React component is silently dropped. Nothing warns, in the console or
+anywhere else; the page simply looks emptier than every core page around it. This
+template shipped exactly that mistake until a run of it against a real core was
+looked at, which is the only way that class of thing is ever found.
+
 **It is curated and closed, not a re-export of core's component library.** Adding
 to it is a minor version bump, and so is adding an optional prop to a member;
 changing an existing prop is a major one.