feat(serve): show the engine's metrics and log in a full-screen view - #177

spinloop serve on a terminal opens a full-screen view of the engine: its metrics above, its log below — piped runs are unchanged.

Summary

• Running serve on a terminal opens a full-screen view: the engine's metrics (state and uptime, what is served, CPU, RAM and GPU as a gauge with its history beneath, and the token counters) above a tailed, followed log, with the view's keys in the footer
• The log follows new output, scrolls with the arrows (a page at a time with pgup/pgdown), and f pauses and resumes the follow without losing a line; scrolled away from the tail the window stays put while new lines accrue behind it
• Leaving the view (q or Ctrl+C) stops the engine through the supervisor, and serve exits with the engine's exit status — an engine that fails on its own takes serve down with it
• Off a terminal nothing changes: the engine's output is forwarded to serve's own stdio and the printed command stays on stdout; on a terminal the view owns stdout, so the command goes to stderr. --dry-run never opens the view
• With --api, the control API's log endpoint serves the captured engine log rather than reporting the log missing
• docs/commands/serve.md documents the view, its keys, and the terminal/non-terminal split

Implementation details

• runServe opens the view only when !dryRun && stdoutIsTerminal(); the engine's metrics endpoint is switched on for any supervised run so the view has its readings, and the printed command is the one that runs
• The view and serve --api share one supervised-foreground construction (startSupervisedForeground): the engine under the daemon's supervisor, its output captured to daemon/engine.log, the control API beside it when asked. runServeForegroundAPI and runServeView are thin wrappers over it
• The view reuses the fleet dashboard's rendering and cadence — the 2s metrics tick, the 3s log poll, the same stale rule, the same series formats — so a number worded in the view is one the dashboard would word the same way