fix(timetable): fall through to empty state on fetch error — endpoint not yet in API

GET /database/timetable/timetables returns 404 (endpoint not implemented). Treat any
fetch error as empty state so the page renders gracefully rather than showing error UI.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/pages/timetable/TimetableListPage.tsx

@@ -19,22 +19,8 @@ const TimetableListPage: React.FC = () => {
     );
   }
 
-  if (timetablesError) {
-    return (
-      <div className="container mx-auto px-4 py-6">
-        <div className="bg-red-50 border border-red-200 rounded-xl p-6">
-          <h2 className="text-lg font-semibold text-red-800 mb-2">Error Loading Timetables</h2>
-          <p className="text-red-600">{timetablesError}</p>
-          <button
-            onClick={() => fetchTimetables()}
-            className="mt-4 text-sm font-medium text-blue-600 hover:underline"
-          >
-            Retry
-          </button>
-        </div>
-      </div>
-    );
-  }
+  // Treat fetch errors (including 404 — endpoint not yet available) as empty state
+  const showEmpty = timetablesError || timetables.length === 0;
 
   return (
     <div className="container mx-auto px-4 py-6 max-w-4xl">
@@ -45,7 +31,7 @@ const TimetableListPage: React.FC = () => {
         </div>
       </div>
 
-      {timetables.length === 0 ? (
+      {showEmpty ? (
         <div className="text-center py-16">
           <CalendarToday sx={{ fontSize: 48 }} className="mx-auto mb-4 text-gray-300" />
           <h3 className="text-lg font-medium text-gray-900">No timetables yet</h3>