Move bootstrap injection from experimental.chat.system.transform to
experimental.chat.messages.transform, prepending to the first user
message instead of adding a system message.
This avoids two issues:
- System messages repeated every turn inflate token usage (#750)
- Multiple system messages break Qwen and other models (#894)
Tested on OpenCode 1.3.2 with Claude Sonnet 4.5 — brainstorming skill
fires correctly on "Let's make a React to do list" prompt.
0a1124ba53