Dashboard: Stop repeating the same values on the charging card

[d4rken]

What changed

The charging card on the dashboard kept saying the same thing over and over. On a phone parked at its charge limit it managed to state "80%" six separate times in one card, and the temperature three times.

• The range row is gone. How long you have been charging now sits in the card's title row next to the arrow, where it costs no extra height.
• The charge range moved into the graph's key, and it now describes the whole session. The card only keeps recent history for the graph, so on a long charge the old range quietly narrowed from something like "40→80%" to "79→80%" while it was still the same charge.
• The compact graph no longer prints values at the ends of its lines. The line just above already shows the current level, power and temperature, and those end values trailed slightly behind it.
• The graph no longer draws when nothing is moving. A phone holding at its limit produced flat lines that looked like a real trend but actually meant "there is nothing to plot".
• Play Store screenshots are regenerated to match.

Technical Context

Why the range is stated by the host, not the chart. The dashboard's live curve is a bounded recent window (300 samples decimated to 60), so its own span is not the session's. StatsCurveChart.percentRangeLabel therefore defaults to the plotted span but accepts an explicit null meaning "no range" — without that distinction, one legend entry would mean two different things depending on whether the host had data. The hub teaser passes null because its headline already carries the range; the dashboard card passes the session range.

Why headerStatus is a String, not a slot. The header sits inside the card's own click target, so interactive content there would have to opt out of the surface tap; typing it as text makes that impossible rather than merely discouraged. AmplyCardHeader floats trailing content and reports only the title's height, which is why this costs nothing vertically. It gained a reserved minimum title width, and the status is weighted so the chevron is measured first — StatsFormat.duration never rolls over into days, so 123h 59m is reachable and would otherwise starve the title or the arrow.

Why the curve gate needs adjacent variation. LineChart breaks its path at nulls, so [40, null, 41] is two one-point segments that draw nothing — "two distinct values somewhere" would have passed. And flat series matter because a zero-range series self-normalizes to the canvas midpoint: several of them stack into a convincing-looking trend that is really the "no range" fallback.

Accessibility. Compact charts stop describing their endpoints too, not just hiding the labels — otherwise the same stale-by-one-tick contradiction just moves into the screen reader. The legend is real text and is already read aloud.

The shared clock. Both live surfaces now use one rememberLiveElapsedMillis. Its first tick aligns to the next whole session-minute, because a fixed minute-long delay starting at 2m59s would hold the curve back until 3m59s. It also reads the clock on composition instead of trusting the caller's captured value, so a card scrolling back into the lazy list does not re-enter holding a stale timestamp.

Screenshot fixtures. DashboardScreen gained an injectable clock so a fixture can render a live session at a believable age instead of "0m". The fixture curve was also made non-linear — three linear series self-normalize to identical shapes and drew exactly on top of each other.

Review guidance

The states with no chart — the first three minutes of a session, a flat limit hold, null-gapped data — deliberately show no range at all. That is the accepted cost of reclaiming the row, and there is a test pinning it rather than leaving it implicit.

Draft: unit tests, lint and both assemblies pass, but this has not had a device pass yet.