feat(detail): show pupil gender split on school detail pages

Upgrades the existing "Pupils" stat to include a compact split bar and
percentage hint for mixed schools (single-sex schools already carry a
"Boys's/Girls's school" badge, so the split would be redundant).

Wires fact_pupil_characteristics into the API: new SQLAlchemy model and
a real census block in /api/schools/{urn} replacing the prior null stub.

On the primary detail page the inline "Pupils: 241" text is replaced by
a richer block (display number + bar + "52% girls · 48% boys"). On the
secondary detail page the existing "Total pupils" hero stat card grows
the bar and hint beneath the number. Both fall back to the previous
text-only rendering when census gender data is missing.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/data_loader.py

@@ -15,7 +15,7 @@ from .database import SessionLocal, engine
 from .models import (
     DimSchool, DimLocation, KS2Performance,
     FactOfstedInspection, FactParentView, FactAdmissions,
-    FactDeprivation, FactFinance,
+    FactDeprivation, FactFinance, FactPupilCharacteristics,
 )
 from .schemas import SCHOOL_TYPE_MAP
 
@@ -462,8 +462,20 @@ def get_supplementary_data(db: Session, urn: int) -> dict:
         else None
     )
 
-    # Census (fact_pupil_characteristics — minimal until census columns are verified)
-    result["census"] = None
+    # Census (latest year of fact_pupil_characteristics)
+    pc = safe_query(FactPupilCharacteristics, "urn", "year")
+    result["census"] = (
+        {
+            "year": pc.year,
+            "total_pupils": pc.total_pupils,
+            "female_pupils": pc.female_pupils,
+            "male_pupils": pc.male_pupils,
+            "fsm_pct": pc.fsm_pct,
+            "eal_pct": pc.eal_pct,
+        }
+        if pc
+        else None
+    )
 
     # Admissions (latest year)
     a = safe_query(FactAdmissions, "urn", "year")

backend/models.py

@@ -189,6 +189,24 @@ class FactAdmissions(Base):
     admissions_policy = Column(String(100))
 
 
+class FactPupilCharacteristics(Base):
+    """School pupil composition from EES census — one row per URN per year."""
+    __tablename__ = "fact_pupil_characteristics"
+    __table_args__ = (
+        Index("ix_pupil_chars_urn_year", "urn", "year"),
+        MARTS,
+    )
+
+    urn = Column(Integer, primary_key=True)
+    year = Column(Integer, primary_key=True)
+    phase_type_grouping = Column(String(50))
+    total_pupils = Column(Integer)
+    female_pupils = Column(Integer)
+    male_pupils = Column(Integer)
+    fsm_pct = Column(Float)
+    eal_pct = Column(Float)
+
+
 class FactDeprivation(Base):
     """IDACI deprivation index — one row per URN."""
     __tablename__ = "fact_deprivation"