fix(dim_school): expand phase inference with name-based fallback

The case-insensitive "Not Applicable" fix caught schools where GIAS publishes
statutory ages, but some independent schools leave those blank too — they fall
through every branch and end up with null phase and no pill in the UI.

Add a third tier that infers phase from the school name
(Primary/Infant/Junior/Prep vs Secondary/High/Grammar/Senior/Upper) and also
normalise "Not Applicable" handling with trim() + "unknown"/"" exclusion, so
the final else branch can safely return null instead of the catch-all string.

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

pipeline/transform/models/marts/dim_school.sql

@@ -15,12 +15,31 @@ select
     s.local_authority_code * 1000 + s.establishment_number as laestab,
     s.school_name,
     case
-        when s.phase is not null and lower(s.phase) != 'not applicable' then s.phase
+        -- 1. Trust GIAS phase when it's a real value (not the catch-all "Not Applicable")
+        when s.phase is not null
+             and lower(trim(s.phase)) not in ('not applicable', '', 'unknown')
+            then s.phase
+        -- 2. Infer from statutory age range (independent schools still publish these)
         when s.statutory_high_age is not null and s.statutory_high_age <= 11 then 'Primary'
         when s.statutory_low_age is not null and s.statutory_low_age >= 11 then 'Secondary'
         when s.statutory_low_age is not null and s.statutory_high_age is not null
              and s.statutory_low_age < 11 and s.statutory_high_age > 11 then 'All-through'
-        else s.phase
+        -- 3. Fallback: infer from school name (covers independents with missing ages)
+        when s.school_name ilike '%primary%'
+             or s.school_name ilike '%infant%'
+             or s.school_name ilike '%junior%'
+             or s.school_name ilike '%preparatory%'
+             or s.school_name ilike '% prep school%'
+             or s.school_name ilike '% prep %'
+            then 'Primary'
+        when s.school_name ilike '%secondary%'
+             or s.school_name ilike '%high school%'
+             or s.school_name ilike '%grammar%'
+             or s.school_name ilike '%senior school%'
+             or s.school_name ilike '%upper school%'
+            then 'Secondary'
+        -- 4. Give up — leave phase null so the UI renders no pill
+        else null
     end as phase,
     s.school_type,
     s.academy_trust_name,