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.

tests/test_energy_cost.py

@@ -990,6 +990,38 @@ class TestSummarize:
         # Σnet ≈ 2 × 0.4051 = 0.8102
         assert abs(result["metered_net"] - 0.8102) < 1e-6
 
+    def test_metered_kwh_sums(self, energy_db: Session) -> None:
+        """The *_kwh totals sum both tariff registers and are distinct from the money totals."""
+        self._setup_two_periods(energy_db)
+        result = summarize(energy_db, _ts(10, 0), _ts(10, 30))
+
+        # Per period: d1=0.5, d2=1.2 → import 1.7 kWh; r1=0.0, r2=0.1 → export 0.1 kWh.
+        assert abs(result["metered_import_kwh"] - 3.4) < 1e-6, (
+            f"expected Σ(d1+d2) = 2 × 1.7 = 3.4 kWh, got {result['metered_import_kwh']}"
+        )
+        assert abs(result["metered_export_kwh"] - 0.2) < 1e-6, (
+            f"expected Σ(r1+r2) = 2 × 0.1 = 0.2 kWh, got {result['metered_export_kwh']}"
+        )
+        # Regression guard for the mislabelled-unit bug: energy and money totals
+        # must never be conflated (import 3.4 kWh vs 0.8202 EUR of import cost).
+        assert result["metered_import_kwh"] != result["metered_import"]
+        assert result["metered_export_kwh"] != result["metered_export"]
+
+    def test_metered_kwh_excludes_degraded_periods(self, energy_db: Session) -> None:
+        """Degraded periods contribute no kWh, mirroring the money totals."""
+        self._setup_two_periods(energy_db)
+        # Degrade the first period; its kWh must drop out of the totals.
+        row = energy_db.execute(
+            select(EnergyCostPeriod).where(EnergyCostPeriod.period_start == _T0)
+        ).scalar_one()
+        row.degraded = True
+        energy_db.commit()
+
+        result = summarize(energy_db, _ts(10, 0), _ts(10, 30))
+        assert result["degraded_count"] == 1
+        assert abs(result["metered_import_kwh"] - 1.7) < 1e-6
+        assert abs(result["metered_export_kwh"] - 0.1) < 1e-6
+
     def test_period_count(self, energy_db: Session) -> None:
         self._setup_two_periods(energy_db)
         result = summarize(energy_db, _ts(10, 0), _ts(10, 30))
@@ -2708,6 +2740,7 @@ class TestSummarizeSettlementOffset:
 
         expected_keys = {
             "currency", "metered_import", "metered_export", "metered_net",
+            "metered_import_kwh", "metered_export_kwh",
             "fixed_costs", "credits", "total_payable", "period_count",
             "degraded_count", "days",
         }