Fix image uploads and reduce flyer request sizes

app/main.py

@@ -1044,17 +1044,27 @@ def save_image(upload: UploadFile, destination_dir: str, url_prefix: str):
             if image.width * image.height > MAX_IMAGE_PIXELS:
                 raise ValueError("Bildauflösung zu groß")
             image.thumbnail((2400, 2400))
+            has_alpha = image.mode in {"RGBA", "LA"} or (
+                image.mode == "P" and "transparency" in image.info
+            )
             if image.mode not in {"RGB", "RGBA"}:
-                image = image.convert("RGBA" if "transparency" in image.info else "RGB")
+                image = image.convert("RGBA" if has_alpha else "RGB")
             output = BytesIO()
-            image.save(output, format="WEBP", quality=88, method=6)
+            # Nicht jedes Browser-/Proxy-Setup verarbeitet serverseitig
+            # erzeugte WebP-Dateien zuverlässig. Nach der Validierung bleiben
+            # transparente Bilder PNG, normale Bilder werden als JPEG gespeichert.
+            output_format = "PNG" if image.mode == "RGBA" else "JPEG"
+            if output_format == "PNG":
+                image.save(output, format=output_format, optimize=True)
+            else:
+                image.save(output, format=output_format, quality=88, optimize=True)
             safe_contents = output.getvalue()
     except (ValueError, OSError, UnidentifiedImageError, Image.DecompressionBombError):
         return None, HTMLResponse(
             "Die Datei ist kein gültiges oder unterstütztes Bild.", status_code=400
         )
 
-    filename = str(uuid.uuid4()) + ".webp"
+    filename = str(uuid.uuid4()) + (".png" if output_format == "PNG" else ".jpg")
     destination = os.path.join(destination_dir, filename)
     with open(destination, "wb") as file:
         file.write(safe_contents)