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/model/menu_test.go

@@ -0,0 +1,49 @@
+package model_test
+
+import (
+	"testing"
+
+	"github.com/eslider/go-onlyoffice/cmd/office/model"
+)
+
+func TestMenuTreeHasExpectedRoots(t *testing.T) {
+	tree := model.DefaultMenuTree()
+	roots := tree.RootLabels()
+	want := []string{"Projects", "Calendar", "CRM", "Mail", "Documents", "Users"}
+	if len(roots) != len(want) {
+		t.Fatalf("roots=%v want %v", roots, want)
+	}
+	for i, w := range want {
+		if roots[i] != w {
+			t.Fatalf("root[%d]=%q want %q", i, roots[i], w)
+		}
+	}
+}
+
+func TestMenuExpandCollapse(t *testing.T) {
+	tree := model.DefaultMenuTree()
+	if !tree.IsExpandable(0) {
+		t.Fatal("Projects should be expandable")
+	}
+	tree.ToggleExpand(0)
+	if !tree.IsExpanded(0) {
+		t.Fatal("Projects should expand")
+	}
+	tree.ToggleExpand(0)
+	if tree.IsExpanded(0) {
+		t.Fatal("Projects should collapse")
+	}
+}
+
+func TestMenuSelectLeafReturnsSubject(t *testing.T) {
+	tree := model.DefaultMenuTree()
+	// Expand Projects and select "All projects" (first child).
+	tree.ToggleExpand(0)
+	subj, ok := tree.SelectIndex(1)
+	if !ok {
+		t.Fatal("expected leaf subject")
+	}
+	if subj != model.SubjectProjects {
+		t.Fatalf("subject=%v want Projects", subj)
+	}
+}