Adds `bun run profile:idle`: a fully unattended capture of what OpenChamber
does while nobody interacts with it. It reports main-thread busy time, style
recalculation and layout rates, DOM node and listener growth, heap trajectory,
a CPU sampling profile, and per-call-site attribution of timer, animation
frame, and observer work.
Chrome throttles timers and stops producing frames for occluded or backgrounded
windows, which silently reports an idle-looking renderer regardless of what the
page schedules. Launch flags now disable that throttling, and every run measures
frame liveness so a throttled capture is reported as a warning rather than as a
clean result.
CDP launch and client code is shared with the existing browser profiler.
