ESLint

+ Add in ESLint support, with TS and Svelte included.
~ Resolve typing issues in both countdown, and in the healthcheck endpoint

.prettierrc

@@ -3,6 +3,7 @@
   "singleQuote": false,
   "printWidth": 90,
   "plugins": ["prettier-plugin-svelte"],
+  "overrides": [{ "files": "*.svelte", "options": { "parser": "svelte" } }],
   "semi": true,
   "svelteSortOrder": "options-styles-scripts-markup",
   "svelteStrictMode": false,