the URL says which page, not which row

`?page=about` instead of `?page=2`. A URL that names the page can be read, sent to somebody, and still
means the right thing after a database is restored from a dump with different ids — which happened
once in this project already, earlier today.

Home needs a word, because its slug is empty by design: that is the check constraint, and it is what
makes `/` fall out of joining a slug to the root. An empty string is no use in a query parameter that
has to name a page unambiguously, so the admin says `home` — and the site's API now REFUSES that slug,
which is what makes the mapping total in both directions rather than merely usual.

One reserved address costs nothing. Anybody who wanted /home wanted the front page, which they have.

One place maps a page to its URL value and back — pageParam and pageFromParam — so the nav, the detail
panel and the builder cannot disagree about what `?page=` means.

`record` is deleted on every navigation. It belonged to the per-page record panels, which are
unreachable now; nothing reads it, so it was not a bug, but every URL anybody copied carried a
parameter naming a row in a section that no longer exists.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

web/DetailPanel.tsx

@@ -153,12 +153,13 @@ export const DetailPanel = () => {
   const [params] = useSearchParams();
   const raw = params.get('section');
   /*
-    A page selected inside Pages opens the BUILDER, not the list with a row lit up.
+    A page selected inside Pages opens the BUILDER, not the list with a row lit up. By SLUG, so the URL
+    says which page rather than which row — see pageParam in usePages.
 
     The nav says the same thing — Pages is a section and the pages are rows under it — so the detail
     panel follows it. `?page=` is what distinguishes the two, which keeps both addressable.
   */
-  const selectedPage = Number(params.get('page')) || null;
+  const selectedPage = params.get('page');
   const selected: SectionKey = isSectionKey(raw) ? raw : DEFAULT_SECTION;
 
   const { ready, rootSet, loading } = useReady();