feat(frontend): add ESLint and Prettier with Svelte support

- Install eslint, prettier and related plugins
- Add lint and format npm scripts
- Configure eslint.config.js with Svelte + TypeScript rules
- Configure .prettierrc with Svelte plugin
- Fix code to comply with lint rules:
  - Use resolve() for navigation links
  - Use SvelteMap for reactive maps
  - Use writable  instead of  +
  - Remove unused imports and variables

Note: ignoreGoto is set to true due to eslint-plugin-svelte#1327

frontend/src/routes/health/lab-results/+page.svelte

@@ -1,8 +1,9 @@
 <script lang="ts">
 	import { enhance } from '$app/forms';
+	import { goto } from '$app/navigation';
+	import { resolve } from '$app/paths';
 	import type { ActionData, PageData } from './$types';
 	import { m } from '$lib/paraglide/messages.js';
-	import { Badge } from '$lib/components/ui/badge';
 	import { Button } from '$lib/components/ui/button';
 	import { Card, CardContent, CardHeader, CardTitle } from '$lib/components/ui/card';
 	import { Input } from '$lib/components/ui/input';
@@ -16,7 +17,6 @@
 		TableHeader,
 		TableRow
 	} from '$lib/components/ui/table';
-	import { goto } from '$app/navigation';
 
 	let { data, form }: { data: PageData; form: ActionData } = $props();
 
@@ -33,6 +33,12 @@
 	let showForm = $state(false);
 	let selectedFlag = $state('');
 	let filterFlag = $derived(data.flag ?? '');
+
+	function onFlagChange(v: string) {
+		const base = resolve('/health/lab-results');
+		const url = v ? base + '?flag=' + v : base;
+		goto(url, { replaceState: true });
+	}
 </script>
 
 <svelte:head><title>{m["labResults_title"]()} — innercontext</title></svelte:head>
@@ -61,9 +67,7 @@
 		<Select
 			type="single"
 			value={filterFlag}
-			onValueChange={(v) => {
-				goto(v ? `/health/lab-results?flag=${v}` : '/health/lab-results');
-			}}
+			onValueChange={onFlagChange}
 		>
 			<SelectTrigger class="w-32">{filterFlag || m["labResults_flagAll"]()}</SelectTrigger>
 			<SelectContent>