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/View/Cards/CardListItem.vue

@@ -31,7 +31,7 @@
     </div>
     <div class="card__expander" @click.stop>
       <div class="card__expander__close-button">
-        <AppIcon
+        <FlatButton
           icon="xmark"
           @click="collapse()"
         />
@@ -51,6 +51,7 @@ import {
   defineComponent, computed, shallowRef,
 } from 'vue';
 import AppIcon from '@/presentation/components/Shared/Icon/AppIcon.vue';
+import FlatButton from '@/presentation/components/Shared/FlatButton.vue';
 import { injectKey } from '@/presentation/injectionSymbols';
 import ScriptsTree from '@/presentation/components/Scripts/View/Tree/ScriptsTree.vue';
 import { sleep } from '@/infrastructure/Threading/AsyncSleep';
@@ -61,6 +62,7 @@ export default defineComponent({
     ScriptsTree,
     AppIcon,
     CardSelectionIndicator,
+    FlatButton,
   },
   props: {
     categoryId: {