Scaffold a new affiliate-skills skill

Scaffold a new skill for the affiliate-skills repo.

Ask the user for:

1. Skill name (kebab-case, verb-noun format)
2. Which stage? (research, content, blog, landing, distribution)
3. Brief description of what it does

Then:

1. Create skills/{stage}/[skill-name]/SKILL.md from template/SKILL.md
2. Create skills/{stage}/[skill-name]/references/ directory
3. Copy LICENSE to skills/{stage}/[skill-name]/LICENSE.txt
4. Fill in the template with the user's input
5. Remind the user to write at least 2 examples and test with 3 prompts before PR