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/purchases.py

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+from fastapi import APIRouter, Depends, HTTPException, status
+from sqlalchemy.orm import Session
+from pydantic import BaseModel
+from typing import List
+from datetime import datetime
+
+from ..database import get_db
+from .. import models
+from ..dependencies import get_current_user
+
+router = APIRouter()
+
+
+class PurchaseCreate(BaseModel):
+    amount_eur: float
+    price_eur: float
+
+
+class PurchaseOut(BaseModel):
+    id: int
+    amount_eur: float
+    price_eur: float
+    created_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+@router.get("/purchases", response_model=List[PurchaseOut])
+def list_purchases(
+    db: Session = Depends(get_db),
+    current_user: models.User = Depends(get_current_user),
+):
+    return db.query(models.Purchase).filter(models.Purchase.user_id == current_user.id).all()
+
+
+@router.post("/purchases", response_model=PurchaseOut, status_code=status.HTTP_201_CREATED)
+def add_purchase(
+    purchase_in: PurchaseCreate,
+    db: Session = Depends(get_db),
+    current_user: models.User = Depends(get_current_user),
+):
+    purchase = models.Purchase(
+        amount_eur=purchase_in.amount_eur,
+        price_eur=purchase_in.price_eur,
+        user_id=current_user.id,
+    )
+    db.add(purchase)
+    db.commit()
+    db.refresh(purchase)
+    return purchase
+
+
+@router.delete("/purchases/{purchase_id}", status_code=status.HTTP_204_NO_CONTENT)
+def delete_purchase(
+    purchase_id: int,
+    db: Session = Depends(get_db),
+    current_user: models.User = Depends(get_current_user),
+):
+    purchase = db.query(models.Purchase).filter(
+        models.Purchase.id == purchase_id,
+        models.Purchase.user_id == current_user.id,
+    ).first()
+    if not purchase:
+        raise HTTPException(status_code=404, detail="Purchase not found")
+    db.delete(purchase)
+    db.commit()