feat(places): London localities and postcode districts

The GIAS town field puts 1,819 London schools under the single value
'London', so it cannot answer 'schools in Battersea' — a query that appears in
the baseline. No single field can: parliamentary constituency gives Battersea
but not Canary Wharf, admin_ward gives Canary Wharf but not Battersea, and
neither gives Clapham or Shoreditch. So a locality is curated, defined by the
postcode districts it covers, which needs no new ingestion.

A locality may not shadow a published town: the registry raises rather than
silently costing a page that carries real demand. One below the threshold is
logged rather than raising, because a locality can legitimately be too small.

The pipeline seed mirrors the module, with a test guarding the drift — the
same arrangement gias_codes has, and for the same reason: the backend image
does not contain pipeline/.

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

pipeline/transform/seeds/locality_outcodes.csv

@@ -0,0 +1,21 @@
+locality_slug,locality_name,outcodes,region
+battersea,Battersea,SW11,London
+canary-wharf,Canary Wharf,E14,London
+clapham,Clapham,SW4,London
+shoreditch,Shoreditch,EC2A|E1,London
+peckham,Peckham,SE15,London
+brixton,Brixton,SW2|SW9,London
+hackney,Hackney,E5|E8|E9,London
+islington,Islington,N1|N5|N7,London
+camden-town,Camden Town,NW1,London
+greenwich,Greenwich,SE10,London
+wimbledon,Wimbledon,SW19,London
+putney,Putney,SW15,London
+fulham,Fulham,SW6,London
+chiswick,Chiswick,W4,London
+ealing,Ealing,W5|W13,London
+richmond,Richmond,TW9|TW10,London
+stratford,Stratford,E15,London
+walthamstow,Walthamstow,E17,London
+tooting,Tooting,SW17,London
+dulwich,Dulwich,SE21|SE22,London