feat(docs): put-xlsx with excelize cutover workbook

Add internal/xlspipe (github.com/xuri/excelize/v2) and oo docs put-xlsx
to generate multi-sheet budgets with named inputs, SUM/AVG/MIN formulas,
cross-sheet links, Russian labels, and cell comments for OnlyOffice.

Template cutover-portugal: sheets Ввод, Вс 6.09, Чт 3.09, Ср гип, Сводка.
Upload via UploadProjectFileReplacing (--replace default).

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

files.go

@@ -237,6 +237,15 @@ func (c *Client) UploadProjectFile(ctx context.Context, projectID, localPath str
 	return decodeResponseFileEntry(raw)
 }
 
+// UploadProjectFileReplacing upserts by stem|ext in the project Documents folder.
+func (c *Client) UploadProjectFileReplacing(ctx context.Context, projectID, localPath string) (*FileEntry, []int, error) {
+	folderID, err := c.projectFolderID(ctx, projectID)
+	if err != nil {
+		return nil, nil, err
+	}
+	return c.UploadToFolderReplacing(ctx, folderID, localPath)
+}
+
 // GetFile returns file metadata including viewUrl for download.
 func (c *Client) GetFile(ctx context.Context, fileID string) (*FileEntry, error) {
 	if fileID == "" {