fix(strommix): bypass CMS for Energy-Charts production — upstream now needs explicit start/end

Energy-Charts' /public_power endpoint started rejecting requests without
`start` + `end` query params ("HTTP 404: no content available"). The
CMS-cached `strommix_de` external schema cannot pass dynamic time
windows (external-collections v1 has no runtime-vars), so the per-field
fallback chain was effectively dead — when SMARD's load filter lagged
12+ h, both sources returned null and the widget surfaced "Lastwert
nicht verfügbar" with all zeros.

Aggregator now fetches /public_power directly with a 2-hour window,
picks the latest non-null per series, and feeds those values into the
existing per-field fallback. CMS strommix_de schema becomes obsolete
for the widget but stays available for admin debugging.

Same shape as the previous CMS payload, so the fallback merge is
unchanged. Picks `Wind onshore`, `Wind offshore`, `Solar`, `Biomass`,
`Hydro Run-of-River`, `Fossil brown coal / lignite`, `Fossil hard
coal`, `Fossil gas`, `Nuclear`, `Load` from production_types.

src/routes/api/strommix/+server.ts

@@ -46,6 +46,66 @@ type StrommixRaw = {
   measured_at_unix?: number | null;
 };
 
+/**
+ * Fetch Energy-Charts /public_power directly with an explicit time
+ * window. The CMS-cached `strommix_de` schema cannot do this because
+ * external-collections v1 has no runtime-vars; without start/end the
+ * upstream returns 404 ("no content available"). 2-hour window covers
+ * latest 8 quarter-hour slots; we pick the latest non-null per series.
+ */
+type PublicPowerSeries = { name: string; data: (number | null)[] };
+type PublicPowerResp = {
+  unix_seconds?: number[];
+  production_types?: PublicPowerSeries[];
+};
+
+function lastNonNull(arr: (number | null)[]): number | null {
+  for (let i = arr.length - 1; i >= 0; i--) {
+    const v = arr[i];
+    if (typeof v === "number" && Number.isFinite(v)) return v;
+  }
+  return null;
+}
+
+async function fetchEnergyChartsPublicPower(
+  fetcher: typeof fetch
+): Promise<{ data: StrommixRaw | null; stale: boolean }> {
+  try {
+    const nowSec = Math.floor(Date.now() / 1000);
+    const fmt = (sec: number) =>
+      new Date(sec * 1000).toISOString().slice(0, 16) + "Z";
+    const start = fmt(nowSec - 2 * 60 * 60);
+    const end = fmt(nowSec);
+    const url =
+      `https://api.energy-charts.info/public_power?country=de` +
+      `&start=${encodeURIComponent(start)}&end=${encodeURIComponent(end)}`;
+    const res = await fetcher(url, { signal: AbortSignal.timeout(8_000) });
+    if (!res.ok) return { data: null, stale: false };
+    const d = (await res.json()) as PublicPowerResp;
+    const find = (n: string) =>
+      d.production_types?.find((p) => p.name === n)?.data ?? [];
+    const ts = d.unix_seconds ?? [];
+    return {
+      data: {
+        wind_onshore_mw: lastNonNull(find("Wind onshore")),
+        wind_offshore_mw: lastNonNull(find("Wind offshore")),
+        solar_mw: lastNonNull(find("Solar")),
+        biomass_mw: lastNonNull(find("Biomass")),
+        hydro_mw: lastNonNull(find("Hydro Run-of-River")),
+        lignite_mw: lastNonNull(find("Fossil brown coal / lignite")),
+        hard_coal_mw: lastNonNull(find("Fossil hard coal")),
+        gas_mw: lastNonNull(find("Fossil gas")),
+        nuclear_mw: lastNonNull(find("Nuclear")),
+        load_mw: lastNonNull(find("Load")),
+        measured_at_unix: ts[ts.length - 1] ?? null,
+      },
+      stale: false,
+    };
+  } catch {
+    return { data: null, stale: true };
+  }
+}
+
 type CrossborderRaw = {
   flow_at_gw?: number | null;
   flow_be_gw?: number | null;
@@ -129,10 +189,11 @@ async function fetchPriceAtNow(
 export const GET: RequestHandler = async ({ fetch }) => {
   const [smardRaw, energyCharts, cross, priceDe, priceFr] = await Promise.all([
     fetchSmardSnapshot(fetch),
-    // Energy-Charts via the CMS — used as per-field fallback when SMARD
-    // returns null for a specific filter (notably load 410 when SMARD's
-    // pipeline lags more than the production filters).
-    fetchOne<StrommixRaw>("strommix_de", fetch),
+    // Energy-Charts /public_power direct (with explicit time range —
+    // upstream now returns 404 without start/end). Used as per-field
+    // fallback when SMARD's load filter (id 410) lags 12+ hours behind
+    // the production filters and the SMARD snapshot gets discarded.
+    fetchEnergyChartsPublicPower(fetch),
     fetchOne<CrossborderRaw>("crossborder_de", fetch),
     fetchPriceAtNow("DE-LU", fetch),
     fetchPriceAtNow("FR", fetch),