chore(web-player): add prettier and eslint

Flat ESLint config with typescript-eslint and eslint-plugin-svelte,
Prettier with the svelte and tailwindcss plugins. Adds the format and
lint scripts.

Three rules are off on purpose: no-navigation-without-resolve (the app
is served at the root, there is no base path), prefer-svelte-reactivity
(the Set and URLSearchParams uses are local computations, not reactive
state) and no-unused-expressions in .svelte only, where reading a rune
on its own line is how an $effect registers a dependency.

web-player/eslint.config.js

@@ -0,0 +1,41 @@
+import js from '@eslint/js';
+import svelte from 'eslint-plugin-svelte';
+import prettier from 'eslint-config-prettier';
+import globals from 'globals';
+import ts from 'typescript-eslint';
+
+export default ts.config(
+	js.configs.recommended,
+	...ts.configs.recommended,
+	...svelte.configs.recommended,
+	prettier,
+	...svelte.configs.prettier,
+	{
+		languageOptions: {
+			globals: { ...globals.browser, ...globals.node }
+		},
+		rules: {
+			'@typescript-eslint/no-unused-vars': [
+				'error',
+				{ argsIgnorePattern: '^_', varsIgnorePattern: '^_' }
+			],
+			'svelte/no-navigation-without-resolve': 'off',
+			'svelte/prefer-svelte-reactivity': 'off'
+		}
+	},
+	{
+		files: ['**/*.svelte', '**/*.svelte.ts'],
+		languageOptions: {
+			parserOptions: {
+				extraFileExtensions: ['.svelte'],
+				parser: ts.parser
+			}
+		},
+		rules: {
+			'@typescript-eslint/no-unused-expressions': 'off'
+		}
+	},
+	{
+		ignores: ['build/', '.svelte-kit/', 'static/', 'src/lib/api/schema.d.ts']
+	}
+);