fix: feedback author display, sidebar scroll, stage sort by start date

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/prisma/migrations/20260606120000_task_detail_author_name/migration.sql

@@ -0,0 +1 @@
+ALTER TABLE "task_details" ADD COLUMN IF NOT EXISTS "authorName" TEXT;

backend/prisma/schema.prisma

@@ -99,6 +99,7 @@ model TaskDetail {
   taskId      String
   milestoneId String?
   content     String
+  authorName  String?  // 피드백 작성자 표시명 (자유 입력)
   updatedBy   String
   createdAt   DateTime @default(now())
   updatedAt   DateTime @updatedAt

backend/src/routes/details.ts

@@ -5,15 +5,6 @@ import { AppError } from '../middleware/errorHandler';
 
 const router = Router();
 
-async function resolveAuthorId(taskId: string, authorName?: string): Promise<string> {
-  const name = authorName?.toString().trim();
-  if (name) {
-    const user = await prisma.user.findFirst({ where: { name } });
-    if (user) return user.id;
-  }
-  return resolveTaskActorId(taskId);
-}
-
 // POST /api/details/:taskId
 router.post('/:taskId', async (req, res, next) => {
   try {
@@ -30,13 +21,15 @@ router.post('/:taskId', async (req, res, next) => {
       if (!ms) throw new AppError(400, '유효하지 않은 업무 단계입니다.');
     }
 
-    const updatedBy = await resolveAuthorId(taskId, authorName);
+    const displayName = authorName?.toString().trim() || null;
+    const updatedBy = await resolveTaskActorId(taskId);
 
     const detail = await prisma.taskDetail.create({
       data: {
         taskId,
         milestoneId: milestoneId || null,
         content: content.toString().trim(),
+        authorName: displayName,
         updatedBy,
       },
       include: { author: { select: { id: true, name: true } } },