feat: add PostgreSQL extensions and update Dockerfile for initialization

postgres/000_extensions.sql

@@ -0,0 +1,3 @@
+CREATE EXTENSION IF NOT EXISTS citext;
+CREATE EXTENSION IF NOT EXISTS pg_trgm;
+CREATE EXTENSION IF NOT EXISTS pgcrypto;

postgres/Dockerfile

@@ -1 +1,6 @@
-FROM postgres:18.3-alpine
+FROM postgres:18-alpine
+
+COPY 000_extensions.sql /docker-entrypoint-initdb.d/
+
+HEALTHCHECK --interval=10s --timeout=5s --retries=5 \
+  CMD pg_isready -U ${POSTGRES_USER} -d ${POSTGRES_DB}