feat(prediction): add native pvnode.com PV forecast provider

Add PVForecastPVNode, a native 15-minute PV forecast provider for the
pvnode.com V2 API, giving operators another forecast source to choose from
alongside Akkudoktor, VRM and Import.

Two request modes, selected by configuration:
  * site_id set   -> GET /v2/forecast/{site_id}   (a saved, possibly calibrated
    site managed on pvnode.com — the operator enters site id + API key)
  * site_id empty -> POST /v2/forecast/inline      (geometry sent inline from the
    configured pvforecast.planes; no web-app setup required)

V2 response timestamps are site-local wall-clock accompanied by an IANA
timezone; they are resolved to absolute instants before EOS resamples them.
Nullable pv_power (e.g. at night) is treated as 0 W so the optimizer's linear
resampling does not interpolate phantom production across the night.

Registered in pvforecast.py (provider settings + id list) and prediction.py
(singleton, factory list, container union). Adds tests covering timezone
resolution, null handling, both request modes and HTTP-error propagation.

src/akkudoktoreos/prediction/prediction.py

@@ -46,6 +46,7 @@ from akkudoktoreos.prediction.loadvrm import LoadVrm
 from akkudoktoreos.prediction.predictionabc import PredictionContainer
 from akkudoktoreos.prediction.pvforecastakkudoktor import PVForecastAkkudoktor
 from akkudoktoreos.prediction.pvforecastimport import PVForecastImport
+from akkudoktoreos.prediction.pvforecastpvnode import PVForecastPVNode
 from akkudoktoreos.prediction.pvforecastvrm import PVForecastVrm
 from akkudoktoreos.prediction.weatherbrightsky import WeatherBrightSky
 from akkudoktoreos.prediction.weatherclearoutside import WeatherClearOutside
@@ -84,6 +85,7 @@ loadforecast_vrm = LoadVrm()
 loadforecast_import = LoadImport()
 pvforecast_akkudoktor = PVForecastAkkudoktor()
 pvforecast_vrm = PVForecastVrm()
+pvforecast_pvnode = PVForecastPVNode()
 pvforecast_import = PVForecastImport()
 weather_brightsky = WeatherBrightSky()
 weather_clearoutside = WeatherClearOutside()
@@ -105,6 +107,7 @@ def prediction_providers() -> list[
         LoadImport,
         PVForecastAkkudoktor,
         PVForecastVrm,
+        PVForecastPVNode,
         PVForecastImport,
         WeatherBrightSky,
         WeatherClearOutside,
@@ -129,6 +132,7 @@ def prediction_providers() -> list[
         loadforecast_import, \
         pvforecast_akkudoktor, \
         pvforecast_vrm, \
+        pvforecast_pvnode, \
         pvforecast_import, \
         weather_brightsky, \
         weather_clearoutside, \
@@ -149,6 +153,7 @@ def prediction_providers() -> list[
         loadforecast_import,
         pvforecast_akkudoktor,
         pvforecast_vrm,
+        pvforecast_pvnode,
         pvforecast_import,
         weather_brightsky,
         weather_clearoutside,
@@ -174,6 +179,7 @@ class Prediction(PredictionContainer):
             LoadImport,
             PVForecastAkkudoktor,
             PVForecastVrm,
+            PVForecastPVNode,
             PVForecastImport,
             WeatherBrightSky,
             WeatherClearOutside,