test: add PostgreSQL integration harness

scripts/run_postgres_integration.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+repo_root="$(cd "$(dirname "$0")/.." && pwd)"
+container_name="cosmic-clash-postgres-integration"
+database="cosmic_clash_test"
+user="cosmic_clash_test"
+password="cosmic_clash_test"
+
+cleanup() {
+  docker rm -f "$container_name" >/dev/null 2>&1 || true
+}
+trap cleanup EXIT
+
+cleanup
+docker run --rm -d --name "$container_name" \
+  -e POSTGRES_DB="$database" \
+  -e POSTGRES_USER="$user" \
+  -e POSTGRES_PASSWORD="$password" \
+  -p 55432:5432 postgres:17-alpine >/dev/null
+
+for attempt in $(seq 1 30); do
+  if docker exec "$container_name" pg_isready -U "$user" -d "$database" >/dev/null 2>&1; then
+    break
+  fi
+  if [ "$attempt" = 30 ]; then
+    echo "PostgreSQL did not become ready" >&2
+    exit 1
+  fi
+  sleep 1
+done
+
+cd "$repo_root/server"
+COSMIC_CLASH_POSTGRES_DSN="postgres://${user}:${password}@127.0.0.1:55432/${database}?sslmode=disable" \
+  go test -tags integration ./store -count=1