fix(dbt): apply safe_numeric macro to fix EES suppression code 'c' errors

Replace nullif(col, 'z') casts with safe_numeric macro across KS2, KS4,
and admissions staging models. The regex-based macro treats any non-numeric
string (z, c, x, q, u, etc.) as NULL without needing an explicit list.

Also fix FSM_eligible_percent column quoting in stg_ees_admissions — target-
postgres stores mixed-case column names quoted, so unquoted references were
being folded to fsm_eligible_percent by PostgreSQL.

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

pipeline/transform/macros/safe_numeric.sql

@@ -0,0 +1,9 @@
+{#
+  safe_numeric(col)
+  Casts a string column to numeric, treating any non-numeric value as NULL.
+  Handles all EES suppression codes (z, c, x, q, u, etc.) without needing
+  an explicit list — any string that doesn't look like a number becomes NULL.
+#}
+{% macro safe_numeric(col) -%}
+    CASE WHEN {{ col }} ~ '^-?[0-9]+(\.[0-9]+)?$' THEN {{ col }}::numeric ELSE NULL END
+{%- endmacro %}