OPT-23, OPT-28: the day plan counts the sun right, and the night charge covers the expensive-hour shortfall

OPT-23: a state-only forecast is read from now for every span
(Forecast.between since=), so the plan's per-hour sun adds up to the day's
figure, today and tomorrow. Hourly splits are unchanged. The Forecast tab
reads spans the same way.

OPT-28: a Leftover solar battery buys, from the floor, the sum over the
expensive hours of max(0, house - trust x sun), / EFF. Several Leftover
solar batteries hold it together by capacity, the ceiling passes the rest
on, and what none can hold is said (Plan.uncovered_kwh). Home's grid block,
the Batteries line and the mode help (EN + NL) say the level, what it
covers, and that Leftover solar buys only what the sun will not give.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bdqr7PiaHcBnzPituu2yTC

goodwe_controller/app/dayview.py

@@ -42,12 +42,12 @@ def build(c, status: dict, now: datetime, lang: str = "en") -> dict:
 
 def sun_kwh(fc, now, a, b):
     """kWh the forecast gives in `[a, b)`, `a` at or after `now`, or None.
-    Both ends are measured from `now`: `Forecast.between()` reads its start
-    as the moment the "left today" figure was taken, so a span that starts
-    later would be spread over what is left of the bell, not over its own
-    hours (state-only forecasts, DECISIONS/UX-54-forecast-tab.md)."""
-    hi, lo = fc.between(now, b), fc.between(now, a)
-    return None if hi is None or lo is None else max(0.0, hi - lo)
+    Every span is measured from `now` (`Forecast.between(since=)`, OPT-23),
+    as `dayplan.plan()` measures them: a state-only "left today" figure is
+    the sun from the moment it was taken, so a span that starts later must
+    not be spread over what is left of the bell from its own start
+    (DECISIONS/UX-54-forecast-tab.md)."""
+    return fc.between(a, b, since=now)
 
 
 def _times(run):