Add edit purchase feature (date, amount, price)

Backend: PUT /purchases/{id} endpoint accepts updated amount_eur,
price_eur, and created_at. Frontend: inline edit row in PurchaseList
with date picker and number inputs, Save/Cancel actions.

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

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

@@ -16,6 +16,12 @@ class PurchaseCreate(BaseModel):
     price_eur: float
 
 
+class PurchaseUpdate(BaseModel):
+    amount_eur: float
+    price_eur: float
+    created_at: datetime
+
+
 class PurchaseOut(BaseModel):
     id: int
     amount_eur: float
@@ -51,6 +57,27 @@ def add_purchase(
     return purchase
 
 
+@router.put("/purchases/{purchase_id}", response_model=PurchaseOut)
+def update_purchase(
+    purchase_id: int,
+    purchase_in: PurchaseUpdate,
+    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")
+    purchase.amount_eur = purchase_in.amount_eur
+    purchase.price_eur = purchase_in.price_eur
+    purchase.created_at = purchase_in.created_at
+    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,