Add cross-module lesson navigation and admin edit button

- Admin lesson editor now navigates across module boundaries (full course flat list)
- Student lesson view shows "Edit" button for admins linking to lesson editor

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

src/components/admin/lesson-editor.tsx

@@ -21,19 +21,18 @@ interface LessonData {
 interface SiblingLesson {
   id: string;
   title: string;
+  moduleId: string;
 }
 
 export function LessonEditor({
   lesson,
   courseId,
-  moduleId,
   courseSlug,
   prevLesson,
   nextLesson,
 }: {
   lesson: LessonData;
   courseId: string;
-  moduleId: string;
   courseSlug: string;
   prevLesson?: SiblingLesson | null;
   nextLesson?: SiblingLesson | null;
@@ -156,8 +155,8 @@ export function LessonEditor({
     }
   }
 
-  function navigateTo(lessonId: string) {
-    router.push(`/admin/courses/${courseId}/modules/${moduleId}/lessons/${lessonId}`);
+  function navigateTo(target: SiblingLesson) {
+    router.push(`/admin/courses/${courseId}/modules/${target.moduleId}/lessons/${target.id}`);
   }
 
   return (
@@ -213,18 +212,18 @@ export function LessonEditor({
           <div className="flex items-center gap-1">
             <button
               type="button"
-              onClick={() => prevLesson && navigateTo(prevLesson.id)}
+              onClick={() => prevLesson && navigateTo(prevLesson)}
               disabled={!prevLesson}
-              title={prevLesson ? `← ${prevLesson.title}` : "Первый урок в модуле"}
+              title={prevLesson ? `← ${prevLesson.title}` : "Первый урок курса"}
               className="btn-aubade flex items-center gap-1 px-2 py-2 text-sm disabled:opacity-30"
             >
               <ChevronLeft size={14} />
             </button>
             <button
               type="button"
-              onClick={() => nextLesson && navigateTo(nextLesson.id)}
+              onClick={() => nextLesson && navigateTo(nextLesson)}
               disabled={!nextLesson}
-              title={nextLesson ? `${nextLesson.title} →` : "Последний урок в модуле"}
+              title={nextLesson ? `${nextLesson.title} →` : "Последний урок курса"}
               className="btn-aubade flex items-center gap-1 px-2 py-2 text-sm disabled:opacity-30"
             >
               <ChevronRight size={14} />