feat: 迁移数据库至 SQLite 并新增项目文档

- 将 Postgres 数据库替换为 SQLite
- 并同步添加 README 文档以优化项目初始化流程

scripts/init-db.ts

@@ -0,0 +1,22 @@
+import { Database } from 'bun:sqlite'
+import { mkdir } from 'node:fs/promises'
+
+// Ensure data directory exists
+await mkdir('./data', { recursive: true })
+
+const db = new Database('./data/app.db', { create: true })
+db.exec('PRAGMA journal_mode = WAL;')
+
+// Create todo table
+db.exec(`
+  CREATE TABLE IF NOT EXISTS todo (
+    id TEXT PRIMARY KEY,
+    title TEXT NOT NULL,
+    completed INTEGER NOT NULL DEFAULT 0,
+    created_at INTEGER NOT NULL DEFAULT (unixepoch()),
+    updated_at INTEGER NOT NULL DEFAULT (unixepoch())
+  );
+`)
+
+console.log('Database initialized successfully!')
+db.close()