fix: preserve meeting note file metadata

internal/httpapi/payload_userid_test.go

@@ -91,6 +91,30 @@ func TestMeetingPayloadIncludesNamesAndDerivedEndedState(t *testing.T) {
 	}
 }
 
+func TestMeetingNoteFilePayloadKeepsOriginalNameAndExtension(t *testing.T) {
+	now := time.Date(2026, 9, 17, 12, 0, 0, 0, time.UTC)
+	payload := meetingNoteFilePayload(store.MeetingNoteFile{
+		NoteFileID: "mnote_1",
+		FileID:     "file_1",
+		FileName:   "会议纪要.pdf",
+		MIMEType:   "application/pdf",
+		FileSize:   2048,
+		UploaderID: 1,
+		Status:     "active",
+		CreatedAt:  now,
+		UpdatedAt:  now,
+	}, 1)
+	if payload["file_name"] != "会议纪要.pdf" || payload["name"] != "会议纪要.pdf" {
+		t.Fatalf("payload names = file_name:%v name:%v", payload["file_name"], payload["name"])
+	}
+	if payload["file_extension"] != "pdf" {
+		t.Fatalf("file_extension = %v, want pdf", payload["file_extension"])
+	}
+	if payload["mime"] != "application/pdf" || payload["size"] != int64(2048) {
+		t.Fatalf("payload aliases = mime:%v size:%v", payload["mime"], payload["size"])
+	}
+}
+
 func assertNoNumericUserIDs(t *testing.T, value any) {
 	t.Helper()
 	switch typed := value.(type) {