chore: update to ESLint 10

no-useless-assignment joined the recommended set and does not understand runes,
reading every `$bindable()` prop default as a dead store; off for Svelte files.
Carries @eslint/js, @eslint/compat, globals and @types/node with it.

frontend/eslint.config.js

@@ -37,6 +37,13 @@ export default defineConfig(
 		files: ['src/lib/components/ui/**'],
 		rules: { 'svelte/no-navigation-without-resolve': 'off' }
 	},
+	{
+		// no-useless-assignment joined eslint:recommended in ESLint 10, and its flow analysis
+		// does not model runes: it reads `let { ref = $bindable(null) } = $props()` as a value
+		// that is never read. Deleting the default, as it suggests, breaks the binding.
+		files: ['**/*.svelte'],
+		rules: { 'no-useless-assignment': 'off' }
+	},
 	{
 		files: ['**/*.svelte', '**/*.svelte.ts', '**/*.svelte.js'],
 		languageOptions: {