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/convert_test.go

@@ -0,0 +1,19 @@
+package preview_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/eslider/go-onlyoffice/cmd/office/preview"
+)
+
+func TestHTMLToMarkdown(t *testing.T) {
+	html := `<h1>Title</h1><p>Body text</p>`
+	md, err := preview.HTMLToMarkdown(html)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(md, "Title") || !strings.Contains(md, "Body text") {
+		t.Fatalf("conversion failed: %q", md)
+	}
+}