feat: add email confirmation and QR generation

backend/bookings/qr.py

@@ -0,0 +1,29 @@
+import base64
+from io import BytesIO
+
+import qrcode
+
+from .models import Reservation
+
+
+CHECK_IN_PREVIEW_PATH = "/api/check-ins/preview/"
+
+
+def build_check_in_preview_url(raw_check_in_token):
+    return f"{CHECK_IN_PREVIEW_PATH}?token={raw_check_in_token}"
+
+
+def generate_check_in_qr_png(raw_check_in_token):
+    qr_image = qrcode.make(build_check_in_preview_url(raw_check_in_token))
+    buffer = BytesIO()
+    qr_image.save(buffer, format="PNG")
+    return buffer.getvalue()
+
+
+def generate_check_in_qr_base64(*, reservation, raw_check_in_token):
+    if reservation.status != Reservation.Status.CONFIRMED:
+        raise ValueError("QR codes are available only for confirmed reservations.")
+
+    png_bytes = generate_check_in_qr_png(raw_check_in_token)
+    encoded = base64.b64encode(png_bytes).decode("ascii")
+    return f"data:image/png;base64,{encoded}"