web: move all strings to i18n & improve a11y

- omnibox is now fully usable with a screen reader
- back button is now interpreted as such
- subtext now accepts line breaks

web/src/routes/+layout.svelte

@@ -297,5 +297,6 @@
         color: var(--gray);
         line-height: 1.4;
         padding: 0 var(--padding);
+        white-space: pre-line;
     }
 </style>