Unify podcast script and audio generation into single tool

- Merge generate-podcast-script.js and generate-podcast-audio.js into generate-podcast.js
- Add mode flags: --script-only, --audio-only, --all, --file, --module
- Default mode: interactive selection with both script and audio generation
- Update package.json scripts to use unified tool
- Remove deprecated standalone scripts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ofriw