重构项目结构：统一目录层级

- 移除 backend/.git 工作树配置
- 将原根目录文件归入 backend/ 目录
- 新增 app/、frontend/ 等模块
- 保留文件历史（自动识别重命名）

backend/scripts/init-multiple-databases.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+set -e
+set -u
+
+function create_database() {
+    local database=$1
+    echo "Creating database '$database'"
+    psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" <<-EOSQL
+        SELECT 1 FROM pg_database WHERE datname = '$database';
+        DO \$\$
+        BEGIN
+            IF NOT EXISTS (SELECT 1 FROM pg_database WHERE datname = '$database') THEN
+                CREATE DATABASE $database;
+            END IF;
+        END
+        \$\$;
+        GRANT ALL PRIVILEGES ON DATABASE $database TO $POSTGRES_USER;
+EOSQL
+}
+
+if [ -n "$POSTGRES_MULTIPLE_DATABASES" ]; then
+    echo "Multiple database creation requested: $POSTGRES_MULTIPLE_DATABASES"
+    for db in $(echo "$POSTGRES_MULTIPLE_DATABASES" | tr ',' ' '); do
+        create_database "$db"
+    done
+    echo "Multiple databases created"
+fi