fix: show total lessons instead of next milestone in progress text

The progress text was showing "0 of 1" (next milestone) which was confusing.
Now shows "0 of 101" (total lessons) while milestone dots show the milestone progression.

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src/app.js

@@ -320,10 +320,10 @@ function updateProgressDisplay() {
 	// Update progress bar (now shows progress to next milestone)
 	elements.progressFill.style.width = `${stats.progressToNext}%`;
 
-	// Update progress text
+	// Update progress text - show completed of total lessons
 	elements.progressText.textContent = t("progressTextMilestone", {
 		completed: stats.totalCompleted,
-		next: stats.nextMilestone
+		total: stats.totalLessons
 	});
 
 	// Update milestone indicators