fix(test): self-provision the fixture user in ai_credits_reaper.rs

expired_hold_is_swept_and_credits_return_to_available used a hardcoded
UUID assuming a matching users row already existed in whatever
database it ran against, but user_ai_subscriptions.user_id has a FK to
users(id) - against a fresh database (like CI's nxtgauge_test) this
failed with a foreign key violation before the actual sweep/release
logic under test ever ran. Provision it inline instead, matching
ai_credits.rs's make_user() pattern.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/db/tests/ai_credits_reaper.rs

@@ -23,6 +23,17 @@ async fn expired_hold_is_swept_and_credits_return_to_available() {
     let pool = pool().await;
     let user_id = Uuid::parse_str("33333333-3333-3333-3333-333333333333").unwrap();
 
+    // user_ai_subscriptions.user_id has a FK to users(id) - this fixed UUID
+    // isn't a real seeded user in every environment this test might run
+    // against (e.g. a fresh CI database), so provision it here rather than
+    // assuming it pre-exists. Matches ai_credits.rs's make_user() pattern.
+    sqlx::query("INSERT INTO users (id, email, password_hash) VALUES ($1, $2, 'x') ON CONFLICT (id) DO NOTHING")
+        .bind(user_id)
+        .bind(format!("{user_id}@test.local"))
+        .execute(&pool)
+        .await
+        .unwrap();
+
     AiCreditsRepository::ensure_wallet(&pool, user_id).await.unwrap();
 
     let hold = AiCreditsRepository::try_reserve_credits(&pool, user_id, "help_answer", 4, None, None)