Fix button inconsistencies and macOS layout shifts

This commit fixes layout shifts experienced in macOS Safari when
hovering over top menu items. Instead of making text bold — which was
causing layout shifts — the hover effect now changes the text color.
This ensures a consistent UI across different browsers and platforms.

Additionally, this commit fixes the styling of the privacy button
located in the bottom right corner. Previously styled as an `<a>`
element, it is now correctly represented as a `<button>`.

Furthermore, the commit enhances HTML conformity and accessibility by
correctly using `<button>` and `<a>` tags instead of relying on click
interactions on `<span>` elements.

This commit introduces `FlatButton` Vue component and a new
`flat-button` mixin. These centralize button usage and link styles,
aligning the hover/touch reactions of buttons across the application,
thereby creating a more consistent user interface.

src/presentation/components/Scripts/Menu/MenuOptionListItem.vue

@@ -4,23 +4,23 @@
       Parent wrapper allows `MenuOptionList` to safely add content inside
       such as adding content in `::before` block without making it clickable.
     -->
-    <span
-      v-non-collapsing
-      :class="{
-        disabled: !enabled,
-        enabled: enabled,
-      }"
+    <FlatButton
+      :disabled="!enabled"
+      :label="label"
+      flat
       @click="onClicked()"
-    >{{ label }}</span>
+    />
   </span>
 </template>
 
 <script lang="ts">
 import { defineComponent } from 'vue';
 import { NonCollapsing } from '@/presentation/components/Scripts/View/Cards/NonCollapsingDirective';
+import FlatButton from '@/presentation/components/Shared/FlatButton.vue';
 
 export default defineComponent({
   directives: { NonCollapsing },
+  components: { FlatButton },
   props: {
     enabled: {
       type: Boolean,
@@ -48,18 +48,3 @@ export default defineComponent({
   },
 });
 </script>
-
-<style scoped lang="scss">
-@use "@/presentation/assets/styles/main" as *;
-
-.enabled {
-  @include clickable;
-  @include hover-or-touch {
-    font-weight:bold;
-    text-decoration:underline;
-  }
-}
-.disabled {
-  color: $color-primary-light;
-}
-</style>