feat: add Turso (libSQL) storage support for EdgeOne deployment

- Add TursoAdapter implementing DatabaseAdapter interface using @libsql/client
- Add 'turso' storage type to db.ts storage selector (reuses D1Storage)
- Add init-turso.js script for database migration and admin initialization
- Add @libsql/client dependency to package.json
- Update next.config.js to exclude @libsql/client from client-side bundle
- Update edgeone-deploy.yml workflow with TURSO_URL and TURSO_TOKEN secrets
- Update edgeone-build.mjs runtime env keys to include Turso variables
- Update .env.edgeone.example with Turso deployment instructions
- Update README.md with Turso as recommended storage for EdgeOne

Turso provides free SQLite-compatible cloud database (libSQL) with:
- 500 databases, 9GB storage, 1B row reads/month on free tier
- HTTP API compatible with edge/serverless environments
- Full SQLite syntax compatibility, reuses existing migrations

.env.edgeone.example

@@ -6,7 +6,18 @@ BUILD_TARGET=edgeone
 EDGEONE_PAGES=1
 
 # 默认不设置 NEXT_PUBLIC_STORAGE_TYPE，项目会使用默认 localstorage。
-# 如需云端持久化，再自行改为 upstash / redis / postgres 等项目支持的存储。
+# 如需云端持久化，可选用以下存储方案：
+#
+# 方案一：Turso（推荐，免费 SQLite 云数据库）
+#   1. 注册 https://turso.tech 获取免费数据库
+#   2. 设置 NEXT_PUBLIC_STORAGE_TYPE=turso
+#   3. 运行 pnpm init:turso 初始化数据库表结构
+#   4. 配置 TURSO_URL 和 TURSO_TOKEN
+#
+# 方案二：Upstash Redis（KV 存储）
+#   1. 注册 https://upstash.com 获取免费 Redis
+#   2. 设置 NEXT_PUBLIC_STORAGE_TYPE=upstash
+#   3. 配置 UPSTASH_URL 和 UPSTASH_TOKEN
 
 # 管理员账号（请替换）
 USERNAME=admin