feat: add learning-opportunities, learning-goal, and orient skills with auto-plugin
Add three skills from DrCatHicks repos for deliberate skill development
during AI-assisted coding:
- learning-opportunities: interactive exercises after architectural work
- learning-goal: MCII-based goal-setting exercise
- orient: repo orientation generator for onboarding
Add learning-opportunities-auto plugin that shows a toast after git
commits suggesting a learning exercise. Uses home.activation to copy
the plugin into the writable plugins dir, working around Bun's symlink
resolution which breaks import() from Nix store paths.