web/meowbalt: hide meowbalt from screen readers

presence of an image of a cat on the screen doesn't change anything about the ui for vision impaired people. it's unnecessary and potentially annoying to have the description of it read out loud on every screen it's used.

web/src/components/misc/Meowbalt.svelte

@@ -10,7 +10,8 @@
     class="meowbalt {emotion}"
     src="/meowbalt/{emotion}.png"
     height="152"
-    alt={$t(`a11y.meowbalt.${emotion}`)}
+    alt={$t('general.meowbalt')}
+    aria-hidden="true"
 />
 
 <style>