WeKan and FerretDB on one machine can drive CPU high enough to starve other
software. Add a monitor, a governor, and a report. Design: docs/Features/CPU/CPU.md.
Monitor (server/lib/cpuMonitor.js): samples system-wide CPU% from os.cpus()
idle/total deltas on an interval (so it includes WeKan, FerretDB and every other
process). A pure, hysteresis state machine (models/lib/cpuHighTracker.js) turns
the samples into ONLY the START and END of each sustained high-CPU period — two
rows per episode, never a flood. Enters high after 3 consecutive samples >= 85%,
leaves after 3 consecutive < 70%. Each row carries duration, peak, system load,
and what WeKan was doing (setActivity label). Recorded to a new 'cpu' event
stream (server/lib/cpuLog.js).
Governor: cpuMonitor exports isHighCpu() and pauseIfBusy(), so long batch
operations await a short pause and yield the CPU only while the system is busy
(no cost when idle). Wired into the existing-file extension corrector. Tunable
via WEKAN_CPU_* env vars.
Report: 'cpu' added to EVENT_STREAMS; reuses the generic eventStreamReport
(stream="cpu") with search + pagination; a "CPU usage" item is added to the
Admin Panel / Problems side menu (cpuReportTitle i18n).
Tests: cpuHighTracker unit (start/end, duration/peak, no-flap hysteresis;
positive + negative) and cpuMonitorWiring source guards. CHANGELOG + design doc.
