refactor(admissions): rename published_admission_number to places_offered

The staging model aliased EES's total_number_places_offered column as
published_admission_number, but PAN is the school's published capacity
(not exposed by EES at school level) — what we actually have is the
count of places offered in a given admissions round. The misnomer
propagated to the mart, SQLAlchemy model, API response, TS types, and
UI copy ("places per year", "(PAN)").

Rename end-to-end and fix the UI labels:
  - "29 places for 42 first-choice applications"
      → "29 places offered for 42 first-choice applications"
  - "Reception/Year 7 places per year"
      → "Reception/Year 7 places offered"
  - drop the misleading "(PAN)" suffix in the secondary view

Also add a comment in stg_ees_admissions clarifying this is the number
of places offered, not PAN. Requires dbt to rebuild fact_admissions
(marts are materialized as tables) before the backend can start.

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

backend/data_loader.py

@@ -419,7 +419,7 @@ def get_supplementary_data(db: Session, urn: int) -> dict:
         {
             "year": a.year,
             "school_phase": a.school_phase,
-            "published_admission_number": a.published_admission_number,
+            "places_offered": a.places_offered,
             "total_applications": a.total_applications,
             "first_preference_applications": a.first_preference_applications,
             "first_preference_offers": a.first_preference_offers,

backend/models.py

@@ -179,7 +179,7 @@ class FactAdmissions(Base):
     urn = Column(Integer, primary_key=True)
     year = Column(Integer, primary_key=True)
     school_phase = Column(String(50))
-    published_admission_number = Column(Integer)
+    places_offered = Column(Integer)
     total_applications = Column(Integer)
     first_preference_applications = Column(Integer)
     first_preference_offers = Column(Integer)