feat: migrate backend to marts schema, update EES tap for verified datasets

Pipeline:
- EES tap: split KS4 into performance + info streams, fix admissions filename
  (SchoolLevel keyword match), fix census filename (yearly suffix), remove
  phonics (no school-level data on EES), change endswith → in for matching
- stg_ees_ks4: rewrite to filter long-format data and extract Attainment 8,
  Progress 8, EBacc, English/Maths metrics; join KS4 info for context
- stg_ees_admissions: map real CSV columns (total_number_places_offered, etc.)
- stg_ees_census: update source reference, stub with TODO for data columns
- Remove stg_ees_phonics, fact_phonics (no school-level EES data)
- Add ees_ks4_performance + ees_ks4_info sources, remove ees_ks4 + ees_phonics
- Update int_ks4_with_lineage + fact_ks4_performance with new KS4 columns
- Annual EES DAG: remove stg_ees_phonics+ from selector

Backend:
- models.py: replace all models to point at marts.* tables with schema='marts'
  (DimSchool, DimLocation, KS2Performance, FactOfstedInspection, etc.)
- data_loader.py: rewrite load_school_data_as_dataframe() using raw SQL joining
  dim_school + dim_location + fact_ks2_performance; update get_supplementary_data()
- database.py: remove migration machinery, keep only connection setup
- app.py: remove check_and_migrate_if_needed, remove /api/admin/reimport-ks2
  endpoints (pipeline handles all imports)

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

pipeline/dags/school_data_pipeline.py

@@ -120,12 +120,12 @@ with DAG(
     extract_ofsted >> dbt_build_ofsted >> sync_typesense_ofsted
 
 
-# ── Annual DAG (EES: KS2, KS4, Census, Admissions, Phonics) ───────────
+# ── Annual DAG (EES: KS2, KS4, Census, Admissions) ───────────────────
 
 with DAG(
     dag_id="school_data_annual_ees",
     default_args=default_args,
-    description="Annual EES data extraction (KS2, KS4, Census, Admissions, Phonics)",
+    description="Annual EES data extraction (KS2, KS4, Census, Admissions)",
     schedule=None,  # Triggered manually when new releases are published
     start_date=datetime(2025, 1, 1),
     catchup=False,
@@ -140,7 +140,7 @@ with DAG(
 
     dbt_build_ees = BashOperator(
         task_id="dbt_build",
-        bash_command=f"cd {PIPELINE_DIR}/transform && {DBT_BIN} build --profiles-dir . --target production --select stg_ees_ks2+ stg_ees_ks4+ stg_ees_census+ stg_ees_admissions+ stg_ees_phonics+",
+        bash_command=f"cd {PIPELINE_DIR}/transform && {DBT_BIN} build --profiles-dir . --target production --select stg_ees_ks2+ stg_ees_ks4+ stg_ees_census+ stg_ees_admissions+",
     )
 
     sync_typesense_ees = BashOperator(