Address review findings on the fleet metrics page.
Data correctness:
- bucket raw Sentinel samples into epoch-aligned windows (5m/30m/2h per range)
and average them, replacing per-server LTTB. Every server now reports the
same bucket timestamps, so the fleet sums add up point by point instead of
zigzagging between servers (and RX+TX really combine)
- keep only the root mount in disk history, matching HasMetrics::getDiskMetrics
- leave sparkline gaps as null instead of 0, so absent samples read as gaps
Robustness:
- normalize containerMetric in mount()/updatedContainerMetric(), so
/metrics?cmetric=foo no longer throws an undefined array key
- include the server uuid in the container row wire:key; system containers
share one Sentinel id across servers
- round the range start to the minute so the 60s history cache can hit
- cap the Sentinel curl with --max-time 10, so one hung request cannot stall
the serial per-server loop
UI:
- pass the spark time axis on first paint, so tooltips no longer show 1970
- show the active series name (RX/TX) in the server network chart tooltip