OPT-11 P4: solar forecast and day plan

A Home Assistant solar forecast (Forecast.Solar, Solcast or Open-Meteo
shapes) and the add-on's own hourly house use decide, before each cheap
run, whether the sun will fill each battery before the expensive hours.
Leftover solar then buys from the grid only the shortfall; Cheap hours only
skips the part the sun covers; Solar first never grid-charges. No, stale or
failed forecast: P3 option A exactly (12 digests pinned from 5a4cdc2).

Replay (16 recorded days, forecast errors from Elia's day-ahead BE solar):
year-earlier prices P4 19.15 vs P2 19.33 / option A 19.44 / old trade 18.14;
real 2026 prices P4 29.19 vs 32.26 / 32.01 / 31.40 EUR net.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

goodwe_controller/test_batteries_screen.py

@@ -317,6 +317,15 @@ _cases = [
     (dict(role="charge", refused=-1), "refuses_charge"),
     (dict(role="sell", peak=True), "peak"),
     (dict(role="hold", off=True), "off"),
+    # OPT-11 P4: the day plan's word, while holding only.
+    (dict(mode=packmode.LEFTOVER_SOLAR, role="hold", has_at=True,
+          day="sun_fills"), "sun_fills"),
+    (dict(mode=packmode.LEFTOVER_SOLAR, role="hold", day="tops_up"),
+     "tops_up"),
+    (dict(mode=packmode.LEFTOVER_SOLAR, role="hold", day="no_forecast"),
+     "no_forecast"),
+    (dict(mode=packmode.LEFTOVER_SOLAR, role="charge", day="tops_up"),
+     "grid_charge"),
 ]
 _wrong = [(kw, want, why(**kw)) for kw, want in _cases if why(**kw) != want]
 print(f"    {_wrong}")