- Move issue_ref_to_filename and filename_to_issue_ref to kugetsu-index.sh
(where they logically belong, instead of in main kugetsu script)
- Refactor queue daemon to use cmd_start/cmd_continue for session management
- Daemon now checks if worktree/session exists → cmd_continue, else → cmd_start
- Removes ~40 lines of direct opencode session forking logic from daemon
- cmd_start/cmd_continue handle worktree creation, session forking, and tracking
This simplifies the daemon significantly and centralizes session management
in kugetsu-session.sh where it belongs.