feat(office): add Workspace TUI with shared bootstrap and test suite

Introduce the office Bubble Tea browser (module tree, multi-select lists,
markdown preview) alongside oo, with cmd/internal/bootstrap for shared auth,
unit tests across preview/model/ui/fetch, CI build for both binaries, and
GoReleaser archives for office.

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

cmd/office/preview/spreadsheet_test.go

@@ -0,0 +1,32 @@
+package preview_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/eslider/go-onlyoffice/cmd/office/preview"
+)
+
+func TestCSVToMarkdownTable(t *testing.T) {
+	csv := "name,score\nAlice,10\nBob,20\n"
+	md, err := preview.CSVToMarkdownTable([]byte(csv))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(md, "name") || !strings.Contains(md, "Alice") {
+		t.Fatalf("table missing data: %q", md)
+	}
+	if !strings.Contains(md, "|") {
+		t.Fatalf("expected pipe table: %q", md)
+	}
+}
+
+func TestJSONToMarkdown(t *testing.T) {
+	md, err := preview.JSONToMarkdown([]byte(`{"a":1}`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(md, "```") || !strings.Contains(md, `"a"`) {
+		t.Fatalf("expected fenced json: %q", md)
+	}
+}