fix(test): use a fresh random user per ai_credits_reaper.rs run

The fixed UUID (33333333-...) meant every re-run against the same
persistent test database reused the same wallet - any earlier partial
run that panicked before its own capture/release step left
reserved_credits permanently stuck above zero, so this run's fresh
reserve (expected to bring it to exactly 4) actually reads 8, 12, etc.
depending on how many times the suite had previously failed midway.
Matches ai_credits.rs's make_user() pattern (Uuid::new_v4()) instead.

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

crates/db/tests/ai_credits_reaper.rs

@@ -21,12 +21,15 @@ async fn pool() -> PgPool {
 #[tokio::test]
 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();
+    // A fresh random user/wallet every run (matching ai_credits.rs's
+    // make_user() pattern) rather than the fixed UUID this test used to
+    // hardcode - against a persistent test database re-run many times over
+    // a session, reusing one fixed user let earlier partial runs' stuck
+    // reserved_credits (left over whenever the test panicked before its own
+    // capture/release step) silently accumulate onto every subsequent run.
+    let user_id = Uuid::new_v4();
 
-    // user_ai_subscriptions.user_id has a FK to users(id) - this fixed UUID
+    // user_ai_subscriptions.user_id has a FK to users(id).
-    // 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"))