fix: CodeBuddy show-live command to only display content from actual prompt files

- Remove automatic content assembly from project docs when CODEBUDDY.md doesn't exist
- CodeBuddy now behaves consistently with other AI assistants (Claude, etc.)
- Only shows content from ~/.codebuddy/CODEBUDDY.md (user) or ./CODEBUDDY.md (project)
- When no prompt file exists, shows '(No content or file does not exist)'
- Update tests to reflect new function names (create_prompt -> add_prompt, delete_prompt -> remove_prompt)

Author: zhujian0805