Fix frontend Docker build and session ID typing

frontend/app/watchlist/page.tsx

@@ -19,7 +19,7 @@ export default function WatchlistPage() {
       return;
     }
 
-    if (session?.user) {
+    if (session?.user?.id) {
       fetchWatchlist(session.user.id);
     }
   }, [session, isPending, router]);
@@ -38,13 +38,15 @@ export default function WatchlistPage() {
 
   const handleAddStock = async (e: React.FormEvent) => {
     e.preventDefault();
+    const userId = session?.user?.id;
+    if (!userId) return;
 
     try {
       await fetch(`${process.env.NEXT_PUBLIC_API_URL}/api/watchlist`, {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify({
-          user_id: session?.user?.id,
+          user_id: userId,
           ticker: newStock.ticker.toUpperCase(),
           company_name: newStock.company_name,
           sector: newStock.sector
@@ -53,7 +55,7 @@ export default function WatchlistPage() {
 
       setShowAddModal(false);
       setNewStock({ ticker: '', company_name: '', sector: '' });
-      fetchWatchlist(session?.user?.id);
+      fetchWatchlist(userId);
     } catch (error) {
       console.error('Error adding stock:', error);
     }
@@ -61,13 +63,15 @@ export default function WatchlistPage() {
 
   const handleDeleteStock = async (id: number) => {
     if (!confirm('Are you sure you want to remove this stock from watchlist?')) return;
+    const userId = session?.user?.id;
+    if (!userId) return;
 
     try {
       await fetch(`${process.env.NEXT_PUBLIC_API_URL}/api/watchlist/${id}`, {
         method: 'DELETE'
       });
 
-      fetchWatchlist(session?.user?.id);
+      fetchWatchlist(userId);
     } catch (error) {
       console.error('Error deleting stock:', error);
     }