fix: address ESLint warnings and add Vitest configuration

- Add ESLint flat config with Svelte and TypeScript support
- Fix unused variables and component prop naming
- Add Vitest browser testing setup with Playwright
- Configure separate test projects for client and server code

web/src/demo.spec.ts

@@ -0,0 +1,7 @@
+import { describe, it, expect } from 'vitest';
+
+describe('sum test', () => {
+	it('adds 1 + 2 to equal 3', () => {
+		expect(1 + 2).toBe(3);
+	});
+});

web/src/lib/components/NavLink.svelte

@@ -3,7 +3,7 @@
 
 	let {
 		href,
-		icon,
+		icon: Icon,
 		label,
 		active = false,
 		size = 18
@@ -23,6 +23,6 @@
 </script>
 
 <a {href} class={navLinkClass(active)}>
-	<icon {size}></icon>
+	<Icon {size} />
 	<span>{label}</span>
 </a>

web/src/routes/+layout.svelte

@@ -202,7 +202,7 @@
 			</div>
 
 			<div class="absolute right-4 hidden sm:flex gap-4 items-center">
-				{#each sourceLinks as link}
+				{#each sourceLinks as link (link.href)}
 					<a
 						href={link.href}
 						title={link.label}
@@ -266,7 +266,7 @@
 					</button>
 				</div>
 				<div class="flex flex-col gap-3">
-					{#each links as link}
+					{#each links as link (link.href)}
 						<NavLink
 							href={link.href}
 							icon={link.icon}

web/src/routes/+page.svelte

@@ -41,7 +41,7 @@
 		}
 	}
 
-	function handleKeyDown(e: KeyboardEvent) {
+	function handleKeyDown() {
 		if (!gameReady || gameStarted) return;
 		handleInteraction();
 	}

web/src/routes/page.svelte.spec.ts

@@ -0,0 +1,13 @@
+import { page } from 'vitest/browser';
+import { describe, expect, it } from 'vitest';
+import { render } from 'vitest-browser-svelte';
+import Page from './+page.svelte';
+
+describe('/+page.svelte', () => {
+	it('should render h1', async () => {
+		render(Page);
+		
+		const heading = page.getByRole('heading', { level: 1 });
+		await expect.element(heading).toBeInTheDocument();
+	});
+});