Fix Clear Completed button failing on queue items with Jira ticket links

The DELETE /completed endpoint failed with a FK violation when completed
queue items had associated rows in jira_ticket_queue_items. Replaced the
bare DELETE query with a transaction that removes junction table references
before deleting the queue items themselves.

Transaction sequence: BEGIN → SELECT completed IDs → DELETE junction rows →
DELETE queue items → COMMIT, with ROLLBACK on error and client release in
finally block.

backend/routes/ivantiTodoQueue.js

@@ -441,15 +441,43 @@ function createIvantiTodoQueueRouter() {
      * @error 500 Internal server error
      */
     router.delete('/completed', requireAuth(), requireGroup('Admin', 'Standard_User'), async (req, res) => {
+        const client = await pool.connect();
         try {
-            const result = await pool.query(
-                "DELETE FROM ivanti_todo_queue WHERE user_id = $1 AND status = 'complete'",
+            await client.query('BEGIN');
+
+            // Select completed item IDs for this user
+            const { rows: completedRows } = await client.query(
+                "SELECT id FROM ivanti_todo_queue WHERE user_id = $1 AND status = 'complete'",
                 [req.user.id]
             );
-            res.json({ message: 'Completed items cleared.', deleted: result.rowCount });
+
+            if (completedRows.length === 0) {
+                await client.query('COMMIT');
+                return res.json({ message: 'Completed items cleared.', deleted: 0 });
+            }
+
+            const ids = completedRows.map(r => r.id);
+
+            // Delete junction table references first
+            await client.query(
+                'DELETE FROM jira_ticket_queue_items WHERE queue_item_id = ANY($1::int[])',
+                [ids]
+            );
+
+            // Delete the completed queue items
+            const deleteResult = await client.query(
+                'DELETE FROM ivanti_todo_queue WHERE id = ANY($1::int[])',
+                [ids]
+            );
+
+            await client.query('COMMIT');
+            res.json({ message: 'Completed items cleared.', deleted: deleteResult.rowCount });
         } catch (err) {
+            await client.query('ROLLBACK');
             console.error('Error clearing completed queue items:', err);
             res.status(500).json({ error: 'Internal server error.' });
+        } finally {
+            client.release();
         }
     });