Switch from chat.message hook to session.created event for injecting
the using-superpowers skill content. The new approach:
- Injects at session creation via session.prompt() with noReply: true
- Explicitly tells model the skill is already loaded to prevent
redundant use_skill calls
- Consolidates bootstrap generation into getBootstrapContent() helper
- Removes fallback pattern in favor of single implementation
Tested with 10 consecutive test runs and manual skill trigger validation.
8c7826c34d