Fix frontend Docker build and session ID typing

frontend/app/portfolio/page.tsx

@@ -22,7 +22,7 @@ export default function PortfolioPage() {
       return;
     }
 
-    if (session?.user) {
+    if (session?.user?.id) {
       fetchPortfolio(session.user.id);
     }
   }, [session, isPending, router]);
@@ -48,13 +48,15 @@ export default function PortfolioPage() {
 
   const handleAddHolding = async (e: React.FormEvent) => {
     e.preventDefault();
+    const userId = session?.user?.id;
+    if (!userId) return;
 
     try {
       await fetch(`${process.env.NEXT_PUBLIC_API_URL}/api/portfolio`, {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify({
-          user_id: session?.user?.id,
+          user_id: userId,
           ticker: newHolding.ticker.toUpperCase(),
           shares: parseFloat(newHolding.shares),
           avg_cost: parseFloat(newHolding.avg_cost)
@@ -63,7 +65,7 @@ export default function PortfolioPage() {
 
       setShowAddModal(false);
       setNewHolding({ ticker: '', shares: '', avg_cost: '' });
-      fetchPortfolio(session?.user?.id);
+      fetchPortfolio(userId);
     } catch (error) {
       console.error('Error adding holding:', error);
     }
@@ -71,13 +73,15 @@ export default function PortfolioPage() {
 
   const handleDeleteHolding = async (id: number) => {
     if (!confirm('Are you sure you want to delete this holding?')) return;
+    const userId = session?.user?.id;
+    if (!userId) return;
 
     try {
       await fetch(`${process.env.NEXT_PUBLIC_API_URL}/api/portfolio/${id}`, {
         method: 'DELETE'
       });
 
-      fetchPortfolio(session?.user?.id);
+      fetchPortfolio(userId);
     } catch (error) {
       console.error('Error deleting holding:', error);
     }