feat(history): whole-row click target and synced multi-chart hover values

The session list row is now clickable (and shows a pointer cursor)
anywhere across the name/status/duration/avg-stats block instead of
only the name text.

Hovering any metric chart in a session's detail view now shows a value
readout on every other linked chart too, at the same timestamp — not
just the crosshair line — so CPU load, temperature, and RAM at a given
moment read across all charts at once instead of only the one under
the cursor. Values update live as the mouse moves along the timeline.

Refs #175