fix: add transaction() to Database interface

[ductiletoaster]

Problem

The custom Database interface in src/db.ts is missing the transaction() method. This causes a TypeScript compilation error when building from source:

src/store.ts(2142,22): error TS2339: Property 'transaction' does not exist on type 'Database'.

The published npm package works because it ships pre-built dist/ files. But building from a fresh git clone fails.

Fix

Add transaction() to the Database interface:

export interface Database {
  exec(sql: string): void;
  prepare(sql: string): Statement;
  transaction<T extends (...args: any[]) => any>(fn: T): T;  // added
  loadExtension(path: string): void;
  close(): void;
}

Both better-sqlite3 and bun:sqlite support transaction(), so this is simply an omission in the interface definition.

Verified

npm install && npm run build  # ✅ compiles successfully