added label syntax support and highlighting

site/src/jsTest/kotlin/LyngHighlightTest.kt

@@ -20,6 +20,22 @@ import kotlin.test.assertFalse
 import kotlin.test.assertTrue
 
 class LyngHighlightTest {
+    @Test
+    fun highlightsReturnAndLabels() {
+        val md = """
+            ```lyng
+            return 42
+            break@outer null
+            return@fn val
+            ```
+        """.trimIndent()
+        val html = renderMarkdown(md)
+
+        assertTrue(html.contains("hl-kw"), "Expected keyword class for 'return': $html")
+        assertTrue(html.contains("hl-lbl") || html.contains("hl-ann"), "Expected label/annotation class for @outer/@fn: $html")
+        assertTrue(html.contains(">>>").xor(true), "Should not contain prompt marker unless expected")
+    }
+
     @Test
     fun highlightsLyngFencedBlock() {
         val md = """