A read-only view per metric and UTC day: every source with readings, its
day value, its place in the person's source priority, and which source
the charts use with the reason. A second card lines two sources up over
30, 90 or 365 days. The pick is explained from the rank the canonical
SQL returns, so the page cannot disagree with the charts. Linked from
the metric pages and from Settings > Source priority.
