Stop Svelte warning about self-closing HTML tags

We'll fix the self-closing tags when we migrate to Svelte 5; in the
meantime, we don't want these warnings to flood the compilation results
and end up hiding other, more important, warnings.

frontend/svelte.config.js

@@ -4,6 +4,7 @@ import { vitePreprocess } from '@sveltejs/vite-plugin-svelte';
 /** @type {import('@sveltejs/kit').Config} */
 const config = {
   compilerOptions: {
+    warningFilter: (warning) => warning.code != 'element_invalid_self_closing_tag',
     enableSourcemap: true
   },
   kit: {

frontend/viewer/svelte.config.js

@@ -8,6 +8,7 @@ const postcssConfig = path.join(__dirname, 'postcss.config.cjs');
 
 export default {
   compilerOptions: {
+    warningFilter: (warning) => warning.code != 'element_invalid_self_closing_tag',
     customElement: true,
   },
   // Consult https://svelte.dev/docs#compile-time-svelte-preprocess