fix: clear completed status when resetting a lesson

- Remove completion badge and reset Run button text in resetSuccessIndicators()
- Remove lesson from completed array in LessonEngine.reset()
- Update sidebar to remove completed class from lesson item
- Update progress display after reset

🤖 Generated with [Claude Code](https://claude.com/claude-code)

src/app.js

@@ -459,6 +459,14 @@ function resetSuccessIndicators() {
 	elements.previewWrapper?.classList.remove("matched");
 	elements.previewWrapper?.classList.remove("completed-glow");
 	elements.previewSection?.classList.remove("matched");
+
+	// Remove completion badge if present
+	const badge = document.querySelector(".completion-badge");
+	if (badge) badge.remove();
+
+	// Reset Run button text
+	const runBtnText = elements.runBtn.querySelector("span");
+	if (runBtnText) runBtnText.textContent = t("run");
 }
 
 function updateEditorForMode(mode) {
@@ -710,6 +718,17 @@ function resetCode() {
 	// Clear hints and success indicators
 	clearHint();
 	resetSuccessIndicators();
+
+	// Update sidebar to remove completed status from this lesson
+	const sidebarItem = document.querySelector(
+		`.lesson-list-item[data-module-id="${engineState.module?.id}"][data-lesson-index="${engineState.lessonIndex}"]`
+	);
+	if (sidebarItem) {
+		sidebarItem.classList.remove("completed");
+	}
+
+	// Update progress display
+	updateProgressDisplay();
 }
 
 function loadRandomTemplate() {

src/impl/LessonEngine.js

@@ -555,6 +555,16 @@ export class LessonEngine {
 			this.userCodeMap.delete(lessonKey);
 			this.saveUserCodeToStorage();
 
+			// Remove lesson from completed list
+			const progress = this.userProgress[this.currentModule.id];
+			if (progress?.completed) {
+				const idx = progress.completed.indexOf(this.currentLessonIndex);
+				if (idx !== -1) {
+					progress.completed.splice(idx, 1);
+					this.saveUserProgress();
+				}
+			}
+
 			this.renderPreview();
 		}
 	}