fix(saas): SQL type cast fixes for E2E relay flow

- key_pool.rs: cast cooldown_until to timestamptz for comparison with NOW()
- key_pool.rs: cast request_count to bigint (INT4→INT8) for sqlx decoding
- service.rs: cast cooldown_until to timestamptz in quota sort query
- scheduler.rs: cast last_seen_at to timestamptz in device cleanup
- totp.rs: use DateTime<Utc> instead of rfc3339 string for updated_at

crates/zclaw-saas/src/auth/totp.rs

@@ -226,7 +226,7 @@ pub async fn verify_totp(
         encrypt_totp_secret(&secret, &enc_key)?
     };
 
-    let now_ts = chrono::Utc::now().to_rfc3339();
+    let now_ts = chrono::Utc::now();
     sqlx::query("UPDATE accounts SET totp_enabled = true, totp_secret = $1, updated_at = $2 WHERE id = $3")
         .bind(&final_secret)
         .bind(&now_ts)
@@ -260,7 +260,7 @@ pub async fn disable_totp(
     }
 
     // 清除 TOTP
-    let now = chrono::Utc::now().to_rfc3339();
+    let now = chrono::Utc::now();
     sqlx::query("UPDATE accounts SET totp_enabled = false, totp_secret = NULL, updated_at = $1 WHERE id = $2")
         .bind(&now)
         .bind(&ctx.account_id)