Add full-stack BTC portfolio web app

Multi-user FastAPI + React app with JWT auth, SQLite storage, and
CoinGecko price integration. Dockerized with docker-compose.

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

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

@@ -0,0 +1,33 @@
+from fastapi import APIRouter, Depends
+from sqlalchemy.orm import Session
+
+from ..database import get_db
+from .. import models
+from ..dependencies import get_current_user
+from ..services.btc import get_btc_price_eur
+
+router = APIRouter()
+
+
+@router.get("/stats")
+def get_stats(
+    db: Session = Depends(get_db),
+    current_user: models.User = Depends(get_current_user),
+):
+    purchases = db.query(models.Purchase).filter(models.Purchase.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
+    current_price = get_btc_price_eur()
+    portfolio_value = total_btc * current_price
+    profit_loss = portfolio_value - total_invested
+
+    return {
+        "total_invested": round(total_invested, 2),
+        "total_btc": round(total_btc, 8),
+        "average_price": round(average_price, 2),
+        "current_price": round(current_price, 2),
+        "portfolio_value": round(portfolio_value, 2),
+        "profit_loss": round(profit_loss, 2),
+    }