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

next.config.js

@@ -136,13 +136,14 @@ const createNextConfig = (phase) => {
       });
     }
 
-    // Exclude better-sqlite3, D1, and Postgres modules from client-side bundle
+    // Exclude better-sqlite3, D1, Postgres, and Turso modules from client-side bundle
     if (!isServer) {
       config.externals = config.externals || [];
       config.externals.push({
         'better-sqlite3': 'commonjs better-sqlite3',
         '@vercel/postgres': 'commonjs @vercel/postgres',
         'pg': 'commonjs pg',
+        '@libsql/client': 'commonjs @libsql/client',
       });
 
       config.resolve.alias = {
@@ -152,6 +153,7 @@ const createNextConfig = (phase) => {
         '@/lib/d1-adapter': false,
         '@/lib/postgres.db': false,
         '@/lib/postgres-adapter': false,
+        '@/lib/turso-adapter': false,
       };
     }