fix(admissions): switch to EES content API + correct publication slug and columns

The EES statistics API only exposes ~13 publications; admissions data is not
among them. Switch to the EES content API (content.explore-education-statistics.
service.gov.uk) which covers all publications.

- ees.py: add get_content_release_id() and download_release_zip_csv() that
  fetch the release ZIP and extract a named CSV member from it
- admissions.py: use corrected slug (primary-and-secondary-school-applications-
  and-offers), correct column names from actual CSV (school_urn,
  total_number_places_offered, times_put_as_1st_preference, etc.), derive
  first_preference_offers_pct from offer/application ratio, filter to primary
  schools only, keep most recent year per URN

Also includes SchoolDetailView UX redesign: parent-first section ordering,
plain-English labels, national average benchmarks, progress score colour
coding, expanded header, quick summary strip, and CSS consolidation.

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

backend/migration.py

@@ -429,10 +429,17 @@ def run_full_migration(geocode: bool = False) -> bool:
         except Exception as e:
             print(f"  Warning: could not save geocode cache: {e}")
 
-    print("Dropping existing tables...")
-    Base.metadata.drop_all(bind=engine)
+    # Only drop the core KS2 tables — leave supplementary tables (ofsted, census,
+    # finance, etc.) intact so a reimport doesn't wipe integrator-populated data.
+    ks2_tables = ["school_results", "schools", "schema_version"]
+    print(f"Dropping core tables: {ks2_tables} ...")
+    inspector = __import__("sqlalchemy").inspect(engine)
+    existing = set(inspector.get_table_names())
+    for tname in ks2_tables:
+        if tname in existing:
+            Base.metadata.tables[tname].drop(bind=engine)
 
-    print("Creating tables...")
+    print("Creating all tables...")
     Base.metadata.create_all(bind=engine)
 
     print("\nLoading CSV data...")