feat(pipeline): add Meltano + dbt + Airflow ELT pipeline scaffold

Replaces the hand-rolled integrator with a production-grade ELT pipeline
using Meltano (Singer taps), dbt Core (medallion architecture), and
Apache Airflow (orchestration). Adds Typesense for search and PostGIS
for geospatial queries.

- 6 custom Singer taps (GIAS, EES, Ofsted, Parent View, FBIT, IDACI)
- dbt project: 12 staging, 5 intermediate, 12 mart models
- 3 Airflow DAGs (daily/monthly/annual schedules)
- Typesense sync + batch geocoding scripts
- docker-compose: add Airflow, Typesense; upgrade to PostGIS
- Portainer stack definition matching live deployment topology

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pipeline/transform/models/marts/dim_location.sql

@@ -0,0 +1,19 @@
+-- Mart: School location dimension — one row per URN, PostGIS-enabled
+-- The geom column is populated by a post-hook or the geocode script.
+
+select
+    s.urn,
+    s.address_line1,
+    s.address_line2,
+    s.town,
+    s.county,
+    s.postcode,
+    s.local_authority_code,
+    s.local_authority_name,
+    s.parliamentary_constituency,
+    s.urban_rural,
+    s.easting,
+    s.northing
+from {{ ref('stg_gias_establishments') }} s
+where s.status = 'Open'
+  and s.postcode is not null