[GAP-007] fix: Remove non-immutable generated column in change_log

PostgreSQL requires generated columns to use immutable expressions.
The executed_at::date cast is not immutable due to timezone dependencies.
Changed to a regular DATE column that can be populated by the trigger.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

schemas/13-audit-triggers-ddl.sql

@@ -60,8 +60,8 @@ CREATE TABLE IF NOT EXISTS audit.change_log (
     -- Timestamp
     executed_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
 
-    -- Para queries eficientes
-    executed_date DATE GENERATED ALWAYS AS (executed_at::date) STORED
+    -- Para queries eficientes (calculado, no generado - por compatibilidad)
+    executed_date DATE
 );
 
 -- Índices para change_log