fix: propagate real message IDs via SSE and fix regenerate model parameter

- Add message_id and user_message_id to SSE done events so frontend
  can replace temp IDs with real DB IDs, fixing "消息不存在" on regenerate
- Replace Body(default=None) with RegenerateRequest Pydantic model for
  proper JSON body parsing, fixing 422 Unprocessable Content
- Frontend always sends model in regenerate request body
- Pass selected model through message-item → regenerateMessage chain
- Various UI refinements to chat sidebar, quick questions, and layout

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/src/app/(main)/course-content/page.tsx

@@ -69,13 +69,6 @@ export default function CourseContentPage() {
       setIsLoading(true);
       setError(null);
       const structure = await courseContentAPI.getCourseContent();
-      console.log("加载的书籍结构:", structure);
-      console.log("章节数量:", structure?.chapters?.length || 0);
-      if (structure?.chapters) {
-        structure.chapters.forEach((chapter, index) => {
-          console.log(`章节 ${index + 1}:`, chapter.title, "节数:", chapter.sections?.length || 0);
-        });
-      }
       setBookStructure(structure);
     } catch (err) {
       console.error("加载课程内容失败:", err);