feat(api): translate GIAS codes to names at the query boundary

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/models.py

@@ -17,11 +17,11 @@ class DimSchool(Base):
 
     urn = Column(Integer, primary_key=True)
     school_name = Column(String(255), nullable=False)
-    phase = Column(String(100))
-    school_type = Column(String(100))
+    phase_code = Column(Integer)
+    school_type_code = Column(Integer)
     academy_trust_name = Column(String(255))
     academy_trust_uid = Column(String(20))
-    religious_character = Column(String(100))
+    religious_character_code = Column(Integer)
     gender = Column(String(20))
     age_range = Column(String(20))
     has_sixth_form = Column(Boolean)
@@ -30,9 +30,9 @@ class DimSchool(Base):
     headteacher_name = Column(String(200))
     website = Column(String(255))
     telephone = Column(String(30))
-    status = Column(String(50))
+    status_code = Column(Integer)
     nursery_provision = Column(Boolean)
-    admissions_policy = Column(String(50))
+    admissions_policy_code = Column(Integer)
     # Denormalised Ofsted summary (updated by monthly pipeline)
     ofsted_grade = Column(Integer)
     ofsted_date = Column(Date)