fix(energy): report real kWh in the cost Summary instead of mislabelled money

The Summary cards labelled `metered_import` / `metered_export` as "(kWh)", but
both fields are monetary totals (Σ import_cost / Σ export_revenue).  Today's
page therefore showed "Import 1.339 kWh" when the meter had actually imported
4.188 kWh — the 1.339 was EUR.  Cross-checked against the DSMR cumulative
registers and Home Assistant: our energy figures were correct all along, only
the label was wrong.

summarize() now also aggregates the metered energy, reusing the already-fetched
non-degraded rows so no extra query is issued:

  metered_import_kwh = Σ (d1_kwh + d2_kwh)
  metered_export_kwh = Σ (r1_kwh + r2_kwh)

The Import/Export cards show kWh as the headline figure and keep the monetary
equivalent as a sub-line, so the split between energy cost and standing
charges/credits behind total_payable stays visible.

The `_kwh` suffix is now the only thing separating energy from money in this
payload, so the docstrings on both summarize() and SummaryResponse call that
out explicitly.

app/integrations/expose.py reads only the money keys, so the HA outbound
sensors are unaffected by the additive fields.

frontend/src/api/schema.d.ts

@@ -2220,7 +2220,9 @@ export interface components {
          * SummaryResponse
          * @description Response for GET /api/energy/costs/summary.
          *
-         *     All monetary values are in ``currency``.
+         *     Monetary values are in ``currency``; the ``*_kwh`` fields are energy totals
+         *     in kWh.  ``metered_import``/``metered_export`` are **money**, not energy —
+         *     only the ``_kwh``-suffixed fields carry kWh.
          *
          *     ``total_payable = metered_net + fixed_costs − credits``
          */
@@ -2229,19 +2231,29 @@ export interface components {
             currency: string;
             /**
              * Metered Import
-             * @description Σ import_cost for non-degraded periods.
+             * @description Σ import_cost for non-degraded periods (money, in `currency`).
              */
             metered_import: number;
             /**
              * Metered Export
-             * @description Σ export_revenue for non-degraded periods.
+             * @description Σ export_revenue for non-degraded periods (money, in `currency`).
              */
             metered_export: number;
             /**
              * Metered Net
-             * @description Σ net_cost for non-degraded periods.
+             * @description Σ net_cost for non-degraded periods (money, in `currency`).
              */
             metered_net: number;
+            /**
+             * Metered Import Kwh
+             * @description Σ (d1_kwh + d2_kwh) for non-degraded periods (energy imported, kWh).
+             */
+            metered_import_kwh: number;
+            /**
+             * Metered Export Kwh
+             * @description Σ (r1_kwh + r2_kwh) for non-degraded periods (energy exported, kWh).
+             */
+            metered_export_kwh: number;
             /**
              * Fixed Costs
              * @description Standing charges (network_fee + management_fee) apportioned over the interval.

frontend/src/energy/CostView.test.tsx

@@ -61,9 +61,13 @@ const COST_PERIOD = {
 
 const SUMMARY = {
   currency: 'EUR',
+  // Money totals and kWh totals are deliberately distinct so the assertions
+  // below prove the cards read the *_kwh fields, not the monetary ones.
   metered_import: 10.5,
   metered_export: 2.3,
   metered_net: 8.2,
+  metered_import_kwh: 33.3,
+  metered_export_kwh: 44.4,
   fixed_costs: 5.0,
   credits: 50.0,
   total_payable: 12.5,
@@ -145,9 +149,14 @@ describe('CostView', () => {
       expect(screen.getByTestId('summary-import')).toBeInTheDocument()
     })
 
-    expect(screen.getByTestId('summary-import')).toHaveTextContent('10.500')
-    expect(screen.getByTestId('summary-export')).toHaveTextContent('2.300')
+    // Main figure is energy (kWh), taken from the *_kwh fields.
+    expect(screen.getByTestId('summary-import')).toHaveTextContent('33.300')
+    expect(screen.getByTestId('summary-export')).toHaveTextContent('44.400')
     expect(screen.getByTestId('summary-total')).toHaveTextContent('12.50')
+
+    // Sub-line carries the monetary equivalent, so money is still visible.
+    expect(screen.getByTestId('summary-import-sub')).toHaveTextContent('10.50 EUR')
+    expect(screen.getByTestId('summary-export-sub')).toHaveTextContent('2.30 EUR')
   })
 
   it('shows recompute confirmation modal on button click', async () => {

frontend/src/energy/CostView.tsx

@@ -77,10 +77,12 @@ function getThisMonthRange(): { start: string; end: string } {
 interface SummaryCardProps {
   label: string
   value: string
+  /** Optional secondary line, e.g. the monetary equivalent of an energy figure. */
+  sub?: string
   testId?: string
 }
 
-function SummaryCard({ label, value, testId }: SummaryCardProps) {
+function SummaryCard({ label, value, sub, testId }: SummaryCardProps) {
   return (
     <Paper withBorder p="sm" data-testid={testId}>
       <Stack gap={4}>
@@ -90,6 +92,11 @@ function SummaryCard({ label, value, testId }: SummaryCardProps) {
         <Text fw={600} size="lg">
           {value}
         </Text>
+        {sub !== undefined && (
+          <Text size="xs" c="dimmed" data-testid={testId ? `${testId}-sub` : undefined}>
+            {sub}
+          </Text>
+        )}
       </Stack>
     </Paper>
   )
@@ -207,12 +214,14 @@ export function CostView() {
           <SimpleGrid cols={{ base: 2, sm: 3 }} spacing="sm" data-testid="cost-summary">
             <SummaryCard
               label="Import (kWh)"
-              value={summaryQuery.data.metered_import.toFixed(3)}
+              value={summaryQuery.data.metered_import_kwh.toFixed(3)}
+              sub={`${summaryQuery.data.metered_import.toFixed(2)} ${currency}`}
               testId="summary-import"
             />
             <SummaryCard
               label="Export (kWh)"
-              value={summaryQuery.data.metered_export.toFixed(3)}
+              value={summaryQuery.data.metered_export_kwh.toFixed(3)}
+              sub={`${summaryQuery.data.metered_export.toFixed(2)} ${currency}`}
               testId="summary-export"
             />
             <SummaryCard

frontend/src/energy/energy-hooks.test.tsx

@@ -83,6 +83,8 @@ const SUMMARY = {
   metered_import: 10.5,
   metered_export: 2.3,
   metered_net: 8.2,
+  metered_import_kwh: 33.3,
+  metered_export_kwh: 44.4,
   fixed_costs: 5.0,
   credits: 50.0,
   total_payable: 12.5,