fix(build): type enrollments array in seed-test-data route

The two enrollment objects had different shapes (one with product_id,
one without), producing a union type that .upsert() rejected as excess
properties, failing the production build. Annotate the array with an
explicit type where product_id is optional.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: guillermoscript

app/api/seed-test-data/route.ts

@@ -70,7 +70,13 @@ export async function POST() {
       })
 
     // Step 4: Create enrollments
-    const enrollments = [
+    const enrollments: Array<{
+      user_id: string
+      course_id: number
+      product_id?: string | null
+      status: string
+      enrolled_at: string
+    }> = [
       {
         user_id: studentUserId,
         course_id: 1,