fix: enable svelte a11y linting and fix violations

frontend/eslint.a11y.config.js

@@ -29,5 +29,22 @@ export default defineConfig(
 				svelteConfig
 			}
 		}
+	},
+	{
+		name: 'svelte:a11y:rules',
+		files: ['**/*.svelte', '**/*.svelte.ts', '**/*.svelte.js'],
+		rules: {
+			// Compile all .svelte files and surface compiler warnings as ESLint errors.
+			// The Svelte 5 compiler has built-in a11y checks (a11y_missing_attribute,
+			// a11y_click_events_have_key_events, a11y_no_static_element_interactions, etc.)
+			// that are enabled by default via accessibilityWarnings: true.
+			'svelte/valid-compile': 'error',
+
+			// Require explicit type attribute on <button> elements
+			'svelte/button-has-type': 'error',
+
+			// Require rel="noopener noreferrer" with target="_blank"
+			'svelte/no-target-blank': 'error'
+		}
 	}
 );