Update A2A CLI guide with complete command reference

- Replace dev install (pip install -e .) with public package (pip install testmu-a2a-cli)
- Add quick reference table listing all 24 CLI subcommands
- Add Workflow Management section (create, list, summary, rename, files, delete, upload-and-generate)
- Add YAML-based prompt setting (--from-file prompt.yaml) to phone agent and prompts sections
- Fix project update commands from python -m cli.main to testmu-a2a

Made-with: Cursor

Author: harsha509