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.