chore(tests): add tester user to prisma seed for cross-user isolation tests

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

prisma/seed.ts

@@ -63,6 +63,26 @@ async function main() {
 
   console.log(`Main user: ${user.username} (id: ${user.id})`)
 
+  // Create tester user for cross-user isolation tests (no products)
+  const testerHash = await bcrypt.hash('tester123', 12)
+  const tester = await prisma.user.upsert({
+    where: { username: 'tester' },
+    update: {},
+    create: {
+      username: 'tester',
+      password_hash: testerHash,
+      is_demo: false,
+      roles: {
+        create: [
+          { role: 'PRODUCT_OWNER' },
+          { role: 'DEVELOPER' },
+        ],
+      },
+    },
+  })
+
+  console.log(`Tester user: ${tester.username} (id: ${tester.id})`)
+
   // Reset demo product data — delete in dependency order to avoid FK violations
   const existingProducts = await prisma.product.findMany({ where: { user_id: demo.id }, select: { id: true } })
   for (const p of existingProducts) {