fix(B03): upload-overview 컬럼명 upload_at으로 수정 (input_files 스키마 정합)

서버 테스트에서 발견 — input_files에는 created_at이 없고 upload_at이다.
upload-overview 응답·Repository 조회 컬럼을 스키마에 맞춤.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

B03_FileInput/B03_FileInput_Repository.py

@@ -304,7 +304,7 @@ async def list_project_input_files(
         await cursor.execute(
             """
             SELECT f.id, f.file_type, f.original_filename, f.file_size_mb, f.status,
-                   f.created_at
+                   f.upload_at
             FROM input_files f
             INNER JOIN (
                 SELECT MAX(id) AS id

B03_FileInput/B03_FileInput_Router.py

@@ -656,7 +656,7 @@ async def get_project_upload_overview(
                     original_filename=str(row["original_filename"]),
                     file_size_mb=float(row["file_size_mb"] or 0.0),
                     status=str(row["status"]),
-                    uploaded_at=str(row["created_at"]) if row.get("created_at") else None,
+                    uploaded_at=str(row["upload_at"]) if row.get("upload_at") else None,
                 )
                 for row in files
             ],