Add lesson progress tracking

- Toggle lesson completion via server action (LessonProgress table)
- "Отметить как пройденный" button on lesson page, turns accent when done
- Course sidebar: progress bar, checkmarks on completed lessons, X/Y counter per module
- Dashboard: progress bar on each course card with completion percentage

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/(student)/courses/[slug]/lessons/[lessonId]/page.tsx

@@ -5,6 +5,7 @@ import { headers } from "next/headers";
 import { auth } from "@/lib/auth";
 import { KinescopePlayer } from "@/components/player/kinescope-player";
 import { LessonContent } from "@/components/student/lesson-content";
+import { LessonCompleteButton } from "@/components/student/lesson-complete-button";
 
 interface Props {
   params: Promise<{ slug: string; lessonId: string }>;
@@ -16,21 +17,23 @@ export default async function LessonPage({ params }: Props) {
   const session = await auth.api.getSession({ headers: await headers() });
   const isAdmin = session?.user.role === "admin";
 
-  const lesson = await prisma.lesson.findUnique({
-    where: { id: lessonId, ...(isAdmin ? {} : { published: true }) },
-    include: {
-      files: { orderBy: { createdAt: "asc" } },
-      module: {
-        include: {
-          course: {
-            include: {
-              modules: {
-                orderBy: { order: "asc" },
-                include: {
-                  lessons: {
-                    where: { published: true },
-                    orderBy: { order: "asc" },
-                    select: { id: true, title: true },
+  const [lesson, progress] = await Promise.all([
+    prisma.lesson.findUnique({
+      where: { id: lessonId, ...(isAdmin ? {} : { published: true }) },
+      include: {
+        files: { orderBy: { createdAt: "asc" } },
+        module: {
+          include: {
+            course: {
+              include: {
+                modules: {
+                  orderBy: { order: "asc" },
+                  include: {
+                    lessons: {
+                      where: { published: true },
+                      orderBy: { order: "asc" },
+                      select: { id: true, title: true },
+                    },
                   },
                 },
               },
@@ -38,11 +41,18 @@ export default async function LessonPage({ params }: Props) {
           },
         },
       },
-    },
-  });
+    }),
+    session && !isAdmin
+      ? prisma.lessonProgress.findUnique({
+          where: { userId_lessonId: { userId: session.user.id, lessonId } },
+        })
+      : null,
+  ]);
 
   if (!lesson || lesson.module.course.slug !== slug) notFound();
 
+  const isCompleted = !!progress;
+
   // Build ordered flat list of all lessons for prev/next
   const allLessons = lesson.module.course.modules.flatMap((m) => m.lessons);
   const idx = allLessons.findIndex((l) => l.id === lessonId);
@@ -108,7 +118,7 @@ export default async function LessonPage({ params }: Props) {
         </div>
       )}
 
-      {/* Prev / Next navigation */}
+      {/* Complete button + Prev/Next navigation */}
       <div
         className="flex items-center justify-between pt-6 mt-6"
         style={{ borderTop: "2px solid var(--border)" }}
@@ -116,23 +126,28 @@ export default async function LessonPage({ params }: Props) {
         {prevLesson ? (
           <Link
             href={`/courses/${slug}/lessons/${prevLesson.id}`}
-            className="btn-aubade text-sm max-w-[45%]"
+            className="btn-aubade text-sm max-w-[40%]"
           >
             ← {prevLesson.title}
           </Link>
         ) : (
           <div />
         )}
+
+        {!isAdmin && (
+          <LessonCompleteButton lessonId={lessonId} slug={slug} isCompleted={isCompleted} />
+        )}
+
         {nextLesson ? (
           <Link
             href={`/courses/${slug}/lessons/${nextLesson.id}`}
-            className="btn-aubade btn-aubade-accent text-sm max-w-[45%] text-right"
+            className="btn-aubade btn-aubade-accent text-sm max-w-[40%] text-right"
           >
             {nextLesson.title} →
           </Link>
         ) : (
           <div className="text-sm" style={{ color: "var(--muted-foreground)" }}>
-            Последний урок курса
+            {isAdmin ? "Последний урок курса" : ""}
           </div>
         )}
       </div>