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>

internal/xlspipe/cutover_portugal_test.go

@@ -0,0 +1,68 @@
+package xlspipe
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/xuri/excelize/v2"
+)
+
+func parseCalcFloat(s string) (float64, error) {
+	s = strings.ReplaceAll(s, ",", "")
+	s = strings.TrimSpace(s)
+	var val float64
+	_, err := fmt.Sscan(s, &val)
+	return val, err
+}
+
+func TestBuildCutoverPortugalWorkbook_Formulas(t *testing.T) {
+	f, err := BuildCutoverPortugalWorkbook(DefaultCutoverPortugal())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+
+	dir := t.TempDir()
+	path := filepath.Join(dir, "cutover.xlsx")
+	if err := Save(f, path); err != nil {
+		t.Fatal(err)
+	}
+	st, err := os.Stat(path)
+	if err != nil || st.Size() < 4096 {
+		t.Fatalf("xlsx too small: %v", err)
+	}
+
+	opened, err := excelize.OpenFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer opened.Close()
+
+	cases := []struct {
+		sheet, cell string
+		want        float64
+		tol         float64
+	}{
+		{SheetDom6, "C8", 1522.89, 0.02},
+		{SheetJue3, "C8", 1549.09, 0.02},
+		{SheetWedHyp, "C11", 1891.95, 0.05},
+		{SheetSummary, "D2", 1522.89, 0.02},
+		{SheetSummary, "D7", 1522.89, 0.02},
+	}
+	for _, tc := range cases {
+		got, err := opened.CalcCellValue(tc.sheet, tc.cell)
+		if err != nil {
+			t.Fatalf("%s!%s calc: %v", tc.sheet, tc.cell, err)
+		}
+		val, err := parseCalcFloat(got)
+		if err != nil {
+			t.Fatalf("%s!%s parse %q: %v", tc.sheet, tc.cell, got, err)
+		}
+		if diff := val - tc.want; diff < -tc.tol || diff > tc.tol {
+			t.Fatalf("%s!%s = %v want ~%v", tc.sheet, tc.cell, val, tc.want)
+		}
+	}
+}