fix(web): allow clearing workspace description and context fields

Previously `|| undefined` prevented sending empty strings, making it
impossible to clear these fields once set. Now always send the current
value so the backend COALESCE correctly updates the column.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/app/(dashboard)/settings/page.tsx

@@ -131,8 +131,8 @@ export default function SettingsPage() {
     try {
       const updated = await api.updateWorkspace(workspace.id, {
         name,
-        description: description || undefined,
-        context: context || undefined,
+        description,
+        context,
       });
       updateWorkspace(updated);
       setSaved(true);