Add course management improvements: tree view, module descriptions, lesson toggles

- SortableModules: add description textarea in edit form, show description in row
- CourseDetailPage: fetch lessons per module, add CourseTree overview section
- ModulePage: fetch sibling modules, pass as otherModules to SortableLessons

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

src/components/admin/sortable-modules.tsx

@@ -22,6 +22,7 @@ import { createModule, deleteModule, updateModule, reorderModules } from "@/app/
 interface Module {
   id: string;
   title: string;
+  description: string | null;
   order: number;
   _count: { lessons: number };
 }
@@ -29,6 +30,7 @@ interface Module {
 function SortableModule({ mod, courseId }: { mod: Module; courseId: string }) {
   const [editing, setEditing] = useState(false);
   const [editValue, setEditValue] = useState(mod.title);
+  const [editDesc, setEditDesc] = useState(mod.description ?? "");
   const [pending, startTransition] = useTransition();
   const { attributes, listeners, setNodeRef, transform, transition, isDragging } =
     useSortable({ id: mod.id });
@@ -69,31 +71,50 @@ function SortableModule({ mod, courseId }: { mod: Module; courseId: string }) {
       </button>
 
       {editing ? (
-        <form onSubmit={handleUpdate} className="flex items-center gap-2 flex-1">
-          <input
-            name="title"
-            value={editValue}
-            onChange={(e) => setEditValue(e.target.value)}
-            autoFocus
-            required
-            className="flex-1 px-2 py-1 text-sm"
-            style={{ border: "2px solid var(--foreground)", background: "var(--background)", outline: "none" }}
+        <form onSubmit={handleUpdate} className="flex flex-col gap-2 flex-1">
+          <div className="flex items-center gap-2">
+            <input
+              name="title"
+              value={editValue}
+              onChange={(e) => setEditValue(e.target.value)}
+              autoFocus
+              required
+              placeholder="Название модуля"
+              className="flex-1 px-2 py-1 text-sm"
+              style={{ border: "2px solid var(--foreground)", background: "var(--background)", outline: "none" }}
+            />
+            <button type="submit" disabled={pending} className="btn-aubade text-xs px-3 py-1 shrink-0">
+              Сохранить
+            </button>
+            <button
+              type="button"
+              onClick={() => { setEditing(false); setEditValue(mod.title); setEditDesc(mod.description ?? ""); }}
+              className="text-xs px-3 py-1 shrink-0"
+              style={{ color: "var(--muted-foreground)" }}
+            >
+              Отмена
+            </button>
+          </div>
+          <textarea
+            name="description"
+            value={editDesc}
+            onChange={(e) => setEditDesc(e.target.value)}
+            placeholder="Описание модуля (опционально)"
+            rows={2}
+            className="w-full px-2 py-1 text-sm resize-none"
+            style={{ border: "1px solid var(--border)", background: "var(--background)", outline: "none" }}
           />
-          <button type="submit" disabled={pending} className="btn-aubade text-xs px-3 py-1">
-            Сохранить
-          </button>
-          <button
-            type="button"
-            onClick={() => { setEditing(false); setEditValue(mod.title); }}
-            className="text-xs px-3 py-1"
-            style={{ color: "var(--muted-foreground)" }}
-          >
-            Отмена
-          </button>
         </form>
       ) : (
         <>
-          <span className="flex-1 font-medium text-sm">{mod.title}</span>
+          <div className="flex-1 min-w-0">
+            <span className="font-medium text-sm">{mod.title}</span>
+            {mod.description && (
+              <p className="text-xs truncate mt-0.5" style={{ color: "var(--muted-foreground)" }}>
+                {mod.description}
+              </p>
+            )}
+          </div>
           <span className="text-xs" style={{ color: "var(--muted-foreground)" }}>
             {mod._count.lessons} {mod._count.lessons === 1 ? "урок" : mod._count.lessons < 5 ? "урока" : "уроков"}
           </span>