Add purchase date picker and sells feature

- Purchase form now includes a date picker (defaults to today)
- New Sell model, CRUD endpoints (/sells), and stats integration
- AddSell and SellList components added to dashboard
- Portfolio chart updated to reflect sells over time

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

btc-portfolio/backend/app/routes/stats.py

@@ -15,17 +15,24 @@ def get_stats(
     current_user: models.User = Depends(get_current_user),
 ):
     purchases = db.query(models.Purchase).filter(models.Purchase.user_id == current_user.id).all()
+    sells = db.query(models.Sell).filter(models.Sell.user_id == current_user.id).all()
 
     total_invested = sum(p.amount_eur for p in purchases)
-    total_btc = sum(p.amount_eur / p.price_eur for p in purchases) if purchases else 0.0
-    average_price = total_invested / total_btc if total_btc > 0 else 0.0
+    total_btc_bought = sum(p.amount_eur / p.price_eur for p in purchases) if purchases else 0.0
+
+    total_btc_sold = sum(s.btc_amount for s in sells)
+    proceeds_eur = sum(s.btc_amount * s.price_eur for s in sells)
+
+    net_btc = total_btc_bought - total_btc_sold
+    net_invested = total_invested - proceeds_eur
+    average_price = net_invested / net_btc if net_btc > 0 else 0.0
     current_price = get_btc_price_eur()
-    portfolio_value = total_btc * current_price
-    profit_loss = portfolio_value - total_invested
+    portfolio_value = net_btc * current_price
+    profit_loss = portfolio_value - net_invested
 
     return {
-        "total_invested": round(total_invested, 2),
-        "total_btc": round(total_btc, 8),
+        "total_invested": round(net_invested, 2),
+        "total_btc": round(net_btc, 8),
         "average_price": round(average_price, 2),
         "current_price": round(current_price, 2),
         "portfolio_value": round(portfolio_value, 2),