fix: update AppHeader styles to remove background image and enhance … (#394)

…transparency

[Storybook
Link](https://wandelbotsgmbh.github.io/wandelbots-js-react-components/overview.html)

Author: stefanwagnerdev

src/components/AppHeader.tsx

@@ -86,9 +86,10 @@ export const AppHeader = externalizeComponent(
           position="static"
           sx={{
             boxShadow: "none",
-            background: (theme) => theme.palette.backgroundPaperElevation?.[1],
-            "& label, a, span": {
-              textWrap: "nowrap",
+            backgroundImage: "none",
+            "& .MuiAppBar-root": {
+              backgroundImage: "none",
+              backgroundColor: "transparent",
             },
             ...sx,
           }}