Refactor Docker entrypoints and remove unused scripts

- Removed custom entrypoint scripts for backend, frontend, and PostgreSQL services from docker-compose files.
- Added a new entrypoint script in the backend and frontend Dockerfiles to handle initialization without relying on host-mounted scripts.
- Updated Dockerfiles to ensure proper permissions for the new entrypoint scripts.
- Enhanced database initialization logic by moving schema and extension creation to the Alembic migration script.

backend/Dockerfile

@@ -42,6 +42,10 @@ COPY requirements.txt .
 # Instalar dependencias Python
 RUN pip install --no-cache-dir -r requirements.txt
 
+# Entrypoint (espera Postgres/Keycloak; no montar desde el host)
+COPY docker-entrypoint.sh /entrypoint.sh
+RUN chmod +x /entrypoint.sh
+
 # Copiar código
 COPY . .
 
@@ -52,5 +56,7 @@ ENV APP_VERSION=${APP_VERSION}
 # Exponer puerto
 EXPOSE 8000
 
+ENTRYPOINT ["/entrypoint.sh"]
+
 # Comando por defecto
 CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000", "--reload"]