fix(places): submit and link the phase variants

/schools/[place]/[phase] shipped as routes but reached nothing. The sitemap
emitted one URL per registry entry and the registry had no phase dimension, so
~950 pages were absent from every sitemap — and PlaceView did not link them
either, leaving them reachable by nothing at all.

That is the query shape the baseline actually showed: 'primary schools in
beccles', 'secondary schools in brentwood'. Publishing the routes without a
path in meant building for the demand and then hiding from it.

Place now carries phase_urns so the per-phase threshold can be applied without
re-querying, the sitemap emits a variant wherever a phase clears the threshold
on its own, and the API exposes the qualifying phases so the place page links
only variants that exist. Outcodes are excluded: nobody searches 'primary
schools in SW11' and those routes do not exist.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015mWQnpye9F299NVRCCSRvj

nextjs-app/components/places/PlaceView.module.css

@@ -106,3 +106,13 @@
   padding: 0;
   margin: 0;
 }
+
+/* Phase variants are separate indexable pages, so the bare place page has to
+   link them — a sitemap entry alone leaves them with no internal path in. */
+.phaseLinks {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 0.5rem 1rem;
+  margin: 0 0 1.25rem;
+  font-size: 0.9375rem;
+}