Meter detail: lead with periods and change, not register totals

The headline tiles were lifetime consumption, a raw reading count and the
register span. None of those answer why someone opens a meter: how much this
month, more or less than last, where the year lands, what it costs. A
cumulative counter's register value is an accident of when the meter was
installed.

MeterPeriodService buckets consumption by calendar month in the instance
timezone -- via date_trunc(... AT TIME ZONE) rather than EF grouping, because a
reading at 00:30 local on 1 January is 23:30 on 31 December in UTC and would be
booked to the wrong month (SDD §10). It reports generation for a generation
counter and consumption otherwise, so a PV meter stops claiming it consumed
0 kWh.

Month- and year-to-date are compared against a projection of the current period
rather than its running total. Three days into a month, "12 kWh vs 340 kWh last
month" reads as a collapse in usage when nothing has changed. The projection is
straight-line on elapsed days -- wrong for anything seasonal, but the honest
reading of "at this rate" -- and the UI marks it with a leading ~.

A 12-month bar strip gives the shape at a glance. A meter with nothing
normalized yet returns an empty history rather than a flat line, which would
look like a meter reading zero.

Register span, reading count and lifetime total move into a collapsed panel.
Still there when needed for an audit, no longer the first thing you see.

Claude-Session: https://claude.ai/code/session_01V6joyergfvVLFEizH1hJLd

src/Infrastructure/Dashboard/MeterDetailModels.cs

@@ -8,6 +8,47 @@ public sealed record ReadingRow(DateTimeOffset Time, double Value, ReadingQualit
 /// <summary>A normalized consumption row for the meter-detail table.</summary>
 public sealed record ConsumptionDetailRow(DateTimeOffset Time, double Amount, ConsumptionKind Kind, ReadingQuality Quality);
 
+/// <summary>One calendar month of a meter's normalized history, bucketed in the instance timezone.</summary>
+public sealed record MeterMonthPoint(DateOnly Month, double Amount, double Cost);
+
+/// <summary>
+/// A meter framed the way it is actually read: what it used this period, how that compares with the
+/// last one, and where the year is heading. Amounts are generation for a generation counter and
+/// consumption otherwise, so <see cref="Label"/> says which.
+/// </summary>
+/// <remarks>
+/// Month- and year-to-date are compared against a <em>projection</em> of the current period rather
+/// than its raw running total: three days into a month, "12 kWh vs 340 kWh last month" reads as a
+/// collapse in usage when nothing has changed. Projections are flagged so the UI can mark them.
+/// </remarks>
+public sealed record MeterPeriodView(
+    string Label,
+    string Unit,
+    string Currency,
+    double MonthToDate,
+    double MonthProjected,
+    double LastMonth,
+    double YearToDate,
+    double YearProjected,
+    double LastYear,
+    double YearToDateCost,
+    double YearProjectedCost,
+    double LastYearCost,
+    bool MonthIsPartial,
+    IReadOnlyList<MeterMonthPoint> Last12Months)
+{
+    /// <summary>Projected month against last month, as a fraction (+0.12 = 12% more). Null if no basis.</summary>
+    public double? MonthChange => Ratio(MonthProjected, LastMonth);
+
+    /// <summary>Projected year against last year, as a fraction. Null if no basis.</summary>
+    public double? YearChange => Ratio(YearProjected, LastYear);
+
+    public bool HasHistory => Last12Months.Count > 0;
+
+    private static double? Ratio(double current, double previous) =>
+        Math.Abs(previous) < 1e-9 ? null : (current - previous) / previous;
+}
+
 /// <summary>A meter lifecycle/correction event row.</summary>
 public sealed record EventRow(DateTimeOffset Time, MeterEventType Type, double? Amount, double? PrevValue, double? NewValue, string? Unit, string? Notes);