feat: add `spinloop work list`

[outofcoffee]

Show the state of the backlog and the active work: every item in the work items file with its record from the state the orchestrator keeps beside it.

• Takes --items <path> (default ./work.yaml), the same file the orchestrator reads; ls as an alias
• Each item's state — backlog, running, done, or failed — with the node a running item runs on, and when it started and ended
• An item with no record in the state shows as backlog; no state file at all (never run) means everything is backlog
• Works whether the orchestrator is running or not
• Plain output a program can consume; decoration only where there is a terminal to draw it on, per the CLI's conventions

Part of the work command family with #206, #208, and #209. Builds on #205.