Use no-dark-mode version of BulmaCSS

While the dark mode works generally, there are various issues with it,
and I don't currently want to spend my time fine-tuning the dark mode.

Note: The bundle is patched to include helpers,
see jgthms/bulma#3736 (comment)

frontend/src/app.html

@@ -4,7 +4,7 @@
     <meta charset="utf-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1" />
     <title>Flugbuech</title>
-    <link rel="stylesheet" href="%sveltekit.assets%/css/bulma.min.css" />
+    <link rel="stylesheet" href="%sveltekit.assets%/css/bulma-no-dark-mode.min.css" />
     <link rel="stylesheet" href="%sveltekit.assets%/css/flugbuech.css" />
     <link rel="stylesheet" href="%sveltekit.assets%/css/fontawesome.min.css" />
     <link rel="stylesheet" href="%sveltekit.assets%/css/fontawesome-solid.min.css" />