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.go

@@ -0,0 +1,65 @@
+package preview
+
+import (
+	"bytes"
+	"encoding/csv"
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	xls "github.com/eslider/go-xls/v2"
+)
+
+// CSVToMarkdownTable parses CSV bytes into a GitHub pipe table markdown string.
+func CSVToMarkdownTable(data []byte) (string, error) {
+	tab, err := parseCSV(data)
+	if err != nil {
+		return "", err
+	}
+	var buf bytes.Buffer
+	if err := xls.WriteMarkdownTable(&buf, tab); err != nil {
+		return "", err
+	}
+	return strings.TrimSpace(buf.String()) + "\n", nil
+}
+
+func parseCSV(data []byte) (xls.Table, error) {
+	r := csv.NewReader(bytes.NewReader(data))
+	r.TrimLeadingSpace = true
+	records, err := r.ReadAll()
+	if err != nil {
+		return xls.Table{}, err
+	}
+	if len(records) == 0 {
+		return xls.Table{}, fmt.Errorf("preview: empty csv")
+	}
+	return xls.Table{Columns: records[0], Rows: records[1:]}, nil
+}
+
+// JSONToMarkdown wraps JSON in a fenced code block for preview.
+func JSONToMarkdown(data []byte) (string, error) {
+	var v any
+	if err := json.Unmarshal(data, &v); err != nil {
+		return "", err
+	}
+	pretty, err := json.MarshalIndent(v, "", "  ")
+	if err != nil {
+		return "", err
+	}
+	return fmt.Sprintf("```json\n%s\n```\n", string(pretty)), nil
+}
+
+// FileBytesToMarkdown picks a preview format based on file extension.
+func FileBytesToMarkdown(name string, data []byte) (string, error) {
+	ext := strings.ToLower(name)
+	switch {
+	case strings.HasSuffix(ext, ".csv"):
+		return CSVToMarkdownTable(data)
+	case strings.HasSuffix(ext, ".json"):
+		return JSONToMarkdown(data)
+	case strings.HasSuffix(ext, ".md"), strings.HasSuffix(ext, ".txt"):
+		return string(data), nil
+	default:
+		return fmt.Sprintf("```\n(binary or unsupported preview for %s, %d bytes)\n```\n", name, len(data)), nil
+	}
+}