fix(admissions): correct first_preference_offer_pct in dbt staging

The staging model was mapping EES column ``proportion_1stprefs_v_totaloffers``
straight onto ``first_preference_offer_pct``. That raw column is not a
percentage — it is a ratio of first-preference applications to total offers
(an oversubscription indicator, >1 means oversubscribed), so OLQH rendered
as "1%" when the true first-choice success rate is 27/42 = 64%.

The frontend display code is not at fault and is not patched here —
data-quality issues must be fixed at the source.

- stg_ees_admissions: compute ``first_preference_offer_pct`` as
  ``100 * number_1st_preference_offers / times_put_as_1st_preference`` —
  of families who listed this school first, the % that received an offer
  (0–100). Guard against divide-by-zero.
- stg_ees_admissions: expose the legitimate EES ratio as the new column
  ``oversubscription_ratio`` (1st-preference applications per place) for
  future use, clearly named.
- fact_admissions, FactAdmissions model, data_loader: propagate the new
  ``oversubscription_ratio`` column.
- SchoolAdmissions type: document both columns inline.
- buildSchoolSummary: reword the oversubscription clause so it reads
  sensibly across the whole 0–100 range (no more "just 64%").
- Hero chip subtitle: clearer phrasing "X% of first-choice applicants
  offered a place".

Requires a dbt run of stg_ees_admissions and fact_admissions on deploy
so the new column materialises.

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

pipeline/transform/models/marts/fact_admissions.sql

@@ -9,6 +9,7 @@ select
     first_preference_applications,
     first_preference_offers,
     first_preference_offer_pct,
+    oversubscription_ratio,
     oversubscribed,
     admissions_policy
 from {{ ref('stg_ees_admissions') }}

pipeline/transform/models/staging/stg_ees_admissions.sql

@@ -29,7 +29,25 @@ renamed as (
         {{ safe_numeric('times_put_as_1st_preference') }}::integer as first_preference_applications,
 
         -- Proportions
-        {{ safe_numeric('proportion_1stprefs_v_totaloffers') }} as first_preference_offer_pct,
+        -- first_preference_offer_pct: of families who listed this school FIRST,
+        -- the percentage that received an offer. 0–100 scale.
+        -- The raw EES column `proportion_1stprefs_v_totaloffers` stores a
+        -- different, misleading figure (first-preference applications divided
+        -- by total offers, i.e. an oversubscription ratio) — do not use it.
+        case
+            when {{ safe_numeric('times_put_as_1st_preference') }} > 0
+                then 100.0
+                     * {{ safe_numeric('number_1st_preference_offers') }}
+                     / {{ safe_numeric('times_put_as_1st_preference') }}
+        end as first_preference_offer_pct,
+
+        -- Oversubscription ratio: 1st-preference applications per place offered.
+        -- >1 means the school is oversubscribed on first preferences.
+        case
+            when {{ safe_numeric('total_number_places_offered') }} > 0
+                then {{ safe_numeric('times_put_as_1st_preference') }}::numeric
+                     / {{ safe_numeric('total_number_places_offered') }}
+        end as oversubscription_ratio,
 
         -- Derived: oversubscribed if 1st-preference applications > places offered
         -- Use already-cast columns to avoid repeating the regex expression