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/eslint.config.js

@@ -0,0 +1,33 @@
+import prettier from 'eslint-config-prettier';
+import svelte from 'eslint-plugin-svelte';
+import globals from 'globals';
+import ts from 'typescript-eslint';
+
+export default [
+	...ts.configs.recommended,
+	...svelte.configs['flat/recommended'],
+	prettier,
+	...svelte.configs['flat/prettier'],
+	{
+		languageOptions: {
+			globals: {
+				...globals.browser,
+				...globals.node
+			}
+		}
+	},
+	{
+		files: ['**/*.svelte'],
+		languageOptions: {
+			parserOptions: {
+				parser: ts.parser
+			}
+		},
+		rules: {
+			'svelte/no-navigation-without-resolve': 'off'
+		}
+	},
+	{
+		ignores: ['build/', '.svelte-kit/', 'dist/', '**/*.cjs', 'static/**']
+	}
+];