Complete Phase 1 of subprocess management in gadget-drone:
- SubProcessService with graceful shutdown (SIGINT→SIGKILL), halt, getLog
- SubprocessTool with create/list/kill/killAll/halt/log commands
- Registered in agent toolbox for build/test/ship/develop modes
- Fixed missing {{process_management_block}} replacement in chat-session.ts
- 34 unit tests across service and tool
- Comprehensive documentation in docs/subprocess.md
