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>
