feat(census): add demographic columns to EES census tap and staging models

tap-uk-ees: EESCensusStream now declares 27 data columns (FSM %, EAL %,
ethnicity breakdowns, pupil counts) with clean Singer field names mapped
from the verbose CSV column names (e.g. '% of pupils known to be eligible
for free school meals' → fsm_pct) via a new _column_renames mechanism on
the base stream class.

stg_ees_census: materialised as table, applies safe_numeric to all
percentage/count columns, filters to numeric URNs.

int_pupil_chars_merged + fact_pupil_characteristics: pass all columns
through from staging (previously stubs with only 3 columns).

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

pipeline/transform/models/marts/fact_pupil_characteristics.sql

@@ -1,8 +1,34 @@
 -- Mart: Pupil characteristics — one row per URN per year
--- TODO: Expand once census data columns are verified and added to staging
 
 select
     urn,
     year,
-    phase_type_grouping
+    phase_type_grouping,
+    total_pupils,
+    female_pupils,
+    male_pupils,
+    full_time_pupils,
+    part_time_pupils,
+    total_boarders,
+    fsm_eligible_n,
+    fsm_pct,
+    eal_pct,
+    young_carer_pct,
+    ethnicity_white_british_pct,
+    ethnicity_white_other_pct,
+    ethnicity_gypsy_roma_pct,
+    ethnicity_mixed_wbc_pct,
+    ethnicity_mixed_wba_pct,
+    ethnicity_mixed_wa_pct,
+    ethnicity_mixed_other_pct,
+    ethnicity_asian_indian_pct,
+    ethnicity_asian_pakistani_pct,
+    ethnicity_asian_bangladeshi_pct,
+    ethnicity_asian_other_pct,
+    ethnicity_black_caribbean_pct,
+    ethnicity_black_african_pct,
+    ethnicity_black_other_pct,
+    ethnicity_chinese_pct,
+    ethnicity_other_pct,
+    ethnicity_unclassified_pct
 from {{ ref('int_pupil_chars_merged') }}