Add data migration script for user-accounts (task 2.5)

Create scripts/migrate-users.ts that:
- Creates a default admin user from DEFAULT_ADMIN_EMAIL/DEFAULT_ADMIN_PASSWORD env vars
- Backfills user_id on all existing rows in charts, annotations, annotation_types,
  span_annotations, span_label_types
- Is idempotent (safe to run multiple times)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/migrate-users.ts

@@ -0,0 +1,89 @@
+/**
+ * Data migration script for user-accounts feature (Task 2.5)
+ *
+ * 1. Creates a default admin user from DEFAULT_ADMIN_EMAIL / DEFAULT_ADMIN_PASSWORD env vars
+ * 2. Backfills user_id on all existing rows in charts, annotations, annotation_types,
+ *    span_annotations, span_label_types to the default admin user's ID
+ *
+ * Idempotent: safe to run multiple times.
+ *
+ * Usage:  DATABASE_URL=... DEFAULT_ADMIN_EMAIL=... DEFAULT_ADMIN_PASSWORD=... npx tsx scripts/migrate-users.ts
+ */
+
+import { Pool } from 'pg';
+import bcrypt from 'bcryptjs';
+
+const SALT_ROUNDS = 12;
+
+async function main() {
+  const DATABASE_URL = process.env.DATABASE_URL;
+  if (!DATABASE_URL) {
+    throw new Error('DATABASE_URL environment variable is required');
+  }
+
+  const adminEmail = process.env.DEFAULT_ADMIN_EMAIL;
+  const adminPassword = process.env.DEFAULT_ADMIN_PASSWORD;
+  if (!adminEmail || !adminPassword) {
+    throw new Error(
+      'DEFAULT_ADMIN_EMAIL and DEFAULT_ADMIN_PASSWORD environment variables are required'
+    );
+  }
+
+  const pool = new Pool({ connectionString: DATABASE_URL });
+
+  try {
+    // ---- Step 1: Upsert default admin user ----
+    console.log(`Creating/finding default admin user: ${adminEmail}`);
+
+    // Check if user already exists
+    const existing = await pool.query(
+      'SELECT id FROM users WHERE email = $1',
+      [adminEmail]
+    );
+
+    let adminUserId: string;
+
+    if (existing.rows.length > 0) {
+      adminUserId = existing.rows[0].id;
+      console.log(`  Admin user already exists (id: ${adminUserId})`);
+    } else {
+      const passwordHash = await bcrypt.hash(adminPassword, SALT_ROUNDS);
+      const inserted = await pool.query(
+        `INSERT INTO users (email, password_hash, name, provider)
+         VALUES ($1, $2, $3, 'credentials')
+         RETURNING id`,
+        [adminEmail, passwordHash, 'Admin']
+      );
+      adminUserId = inserted.rows[0].id;
+      console.log(`  Admin user created (id: ${adminUserId})`);
+    }
+
+    // ---- Step 2: Backfill user_id on all existing rows ----
+    const tables = [
+      'charts',
+      'annotations',
+      'annotation_types',
+      'span_annotations',
+      'span_label_types',
+    ];
+
+    for (const table of tables) {
+      const result = await pool.query(
+        `UPDATE ${table} SET user_id = $1 WHERE user_id IS NULL`,
+        [adminUserId]
+      );
+      console.log(`  ${table}: backfilled ${result.rowCount} rows`);
+    }
+
+    console.log('Migration complete.');
+  } finally {
+    await pool.end();
+  }
+}
+
+main()
+  .then(() => process.exit(0))
+  .catch((err) => {
+    console.error('Migration failed:', err);
+    process.exit(1);
+  });