feat: add PVForecastHomeAssistant provider (#1258)

* feat: add PVForecastHomeAssistant provider

Reads a PV forecast time series directly from a Home Assistant entity
attribute (matching the {"forecast": [{"datetime", "watts"}]} shape
already exposed by common HA PV forecast integrations, e.g. Helios
Forecast and Solcast) and feeds it into pvforecast_ac_power, following
the same self-polling provider pattern as PVForecastVrm.

Closes #1232.

* fix: use MagicMock instead of monkeypatched Response for mypy

requests.Response().json is a typed bound method; reassigning it to a
lambda fails mypy's method-assign check. Use MagicMock(spec=...) instead,
which mocks the response without fighting its static type.

* fix: address PR review on PVForecastHomeAssistant provider

Fixes two issues raised in review on PR #1258:
- _update_data() left stale pvforecast_ac_power values in place when a
  refreshed forecast was empty or shorter than a previous one; it now
  clears the active forecast window before writing and raises instead
  of silently no-op'ing when the response has no usable data.
- pvforecast.homeassistant.entity_id used a "select" widget with no
  manual-entry fallback in EOSdash, leaving it unusable in standalone
  mode where the entity list can't be resolved without SUPERVISOR_TOKEN;
  switched to a plain text field.

Also fills in the config docs and openapi.json for the new
pvforecast.homeassistant.* fields, which were missing from the
original commit.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* fix: preserve retained forecast history when clearing stale entries

The previous fix cleared pvforecast_ac_power from start-of-day, but
PredictionProvider deliberately retains historical records back to
keep_datetime (prediction.historic_hours). Since Home Assistant
forecasts are future-only, that clear wiped out retained history
between midnight and the EMS start on every refresh.

Narrow the clear to [ems_start_datetime, end_datetime) - the actual
active forecast window, DST-adjusted - instead of the day boundary.

Addresses review feedback from @NormannK on PR #1258.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

---------

Co-authored-by: Mathias <mathias@Mathiass-MacBook-Air.local>
Co-authored-by: Mathias <mathias@Mathiass-Air.localdomain>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

openapi.json

@@ -8,7 +8,7 @@
       "name": "Apache 2.0",
       "url": "https://www.apache.org/licenses/LICENSE-2.0.html"
     },
-    "version": "v0.3.0.dev2608221553448643"
+    "version": "v0.3.0.dev2609011977897641"
   },
   "paths": {
     "/v1/admin/cache/clear": {
@@ -10803,6 +10803,10 @@
             "$ref": "#/components/schemas/PVForecastVrmCommonSettings",
             "description": "Victron Remote Management (VRM) provider settings"
           },
+          "homeassistant": {
+            "$ref": "#/components/schemas/PVForecastHomeAssistantCommonSettings",
+            "description": "Home Assistant provider settings"
+          },
           "pvlib": {
             "$ref": "#/components/schemas/PVForecastPVLibCommonSettings",
             "description": "PVLib provider settings"
@@ -10924,6 +10928,10 @@
             "$ref": "#/components/schemas/PVForecastVrmCommonSettings",
             "description": "Victron Remote Management (VRM) provider settings"
           },
+          "homeassistant": {
+            "$ref": "#/components/schemas/PVForecastHomeAssistantCommonSettings",
+            "description": "Home Assistant provider settings"
+          },
           "pvlib": {
             "$ref": "#/components/schemas/PVForecastPVLibCommonSettings",
             "description": "PVLib provider settings"
@@ -11097,6 +11105,93 @@
         "title": "PVForecastForecastSolarCommonSettings",
         "description": "Common settings for the Forecast.Solar PV forecast provider."
       },
+      "PVForecastHomeAssistantCommonSettings": {
+        "properties": {
+          "entity_id": {
+            "type": "string",
+            "title": "Entity Id",
+            "description": "Home Assistant entity providing the PV forecast.",
+            "default": "sensor.pv_forecast",
+            "examples": [
+              "sensor.pv1_power_now"
+            ]
+          },
+          "attribute": {
+            "type": "string",
+            "title": "Attribute",
+            "description": "Entity attribute holding the forecast list.",
+            "default": "forecast",
+            "examples": [
+              "forecast"
+            ]
+          },
+          "datetime_key": {
+            "type": "string",
+            "title": "Datetime Key",
+            "description": "Key for the timestamp in each forecast entry.",
+            "default": "datetime",
+            "examples": [
+              "datetime"
+            ]
+          },
+          "value_key": {
+            "type": "string",
+            "title": "Value Key",
+            "description": "Key for the AC power value in each forecast entry.",
+            "default": "watts",
+            "examples": [
+              "watts"
+            ]
+          },
+          "value_unit": {
+            "type": "string",
+            "enum": [
+              "W",
+              "kW"
+            ],
+            "title": "Value Unit",
+            "description": "Unit of the forecast value. Converted to W internally.",
+            "default": "W",
+            "examples": [
+              "W",
+              "kW"
+            ]
+          },
+          "base_url": {
+            "anyOf": [
+              {
+                "type": "string"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Base Url",
+            "description": "Base URL of the Home Assistant instance. Only required when EOS is not running as a Home Assistant add-on (no SUPERVISOR_TOKEN available).",
+            "examples": [
+              "http://homeassistant.local:8123"
+            ]
+          },
+          "token": {
+            "anyOf": [
+              {
+                "type": "string"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Token",
+            "description": "Long-lived access token for the Home Assistant instance. Only required when EOS is not running as a Home Assistant add-on.",
+            "examples": [
+              null
+            ]
+          }
+        },
+        "type": "object",
+        "title": "PVForecastHomeAssistantCommonSettings",
+        "description": "Common settings for pvforecast data from a Home Assistant entity."
+      },
       "PVForecastImportCommonSettings": {
         "properties": {
           "import_file_path": {