docs: add Knex.js integration guide with installation and setup instructions

Author: mceachen

doc/knex-integration.md

@@ -0,0 +1,73 @@
+# Using with Knex.js
+
+[@photostructure/knex-sqlite](https://github.com/photostructure/knex-sqlite) provides a Knex.js dialect that uses @photostructure/sqlite as the SQLite driver instead of better-sqlite3.
+
+## Installation
+
+```bash
+npm install @photostructure/knex-sqlite @photostructure/sqlite knex
+```
+
+## Setup
+
+```javascript
+const knex = require("knex");
+const Client = require("@photostructure/knex-sqlite");
+
+const db = knex({
+  client: Client,
+  connection: {
+    filename: "./mydb.sqlite",
+  },
+  useNullAsDefault: true,
+});
+```
+
+## Connection options
+
+```javascript
+const db = knex({
+  client: Client,
+  connection: {
+    filename: "./mydb.sqlite",
+    options: {
+      readonly: false, // open as read-only
+      safeIntegers: false, // return BigInt for large integers
+    },
+  },
+  useNullAsDefault: true,
+});
+```
+
+## Features
+
+All standard Knex.js features work: schema building, queries, transactions, joins, aggregations, raw SQL, and `RETURNING` clauses on INSERT/UPDATE.
+
+```javascript
+// Schema
+await db.schema.createTable("users", (table) => {
+  table.increments("id");
+  table.string("name");
+  table.integer("age");
+});
+
+// CRUD
+await db("users").insert({ name: "Alice", age: 30 });
+const users = await db("users").where("age", ">", 25).select("*");
+
+// Transactions
+await db.transaction(async (trx) => {
+  await trx("users").insert({ name: "Bob", age: 25 });
+  await trx("posts").insert({ user_id: 1, title: "Hello" });
+});
+```
+
+## How it works
+
+The dialect extends Knex's built-in `Client_BetterSQLite3` and adapts three things:
+
+1. **Driver**: loads @photostructure/sqlite and calls `enhance()` to add better-sqlite3-style methods
+2. **Statement `.reader` property**: uses `stmt.columns().length > 0` to detect whether a statement returns rows (correctly handles `RETURNING` clauses)
+3. **Binding format**: spreads array bindings as variadic arguments, and maps `safeIntegers()` to `setReadBigInts()`
+
+See the [@photostructure/knex-sqlite README](https://github.com/photostructure/knex-sqlite) for full details.