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/solarfc.py

@@ -76,12 +76,20 @@ class Forecast:
     tomorrow: Day | None
     at: datetime                # when the sensor last reported
 
-    def between(self, t0: datetime, t1: datetime) -> float | None:
+    def between(self, t0: datetime, t1: datetime,
+                since: datetime | None = None) -> float | None:
         """kWh the sun should give between `t0` (now or later) and `t1`.
         None when the span reaches the sunny hours of a day with no
-        forecast (tomorrow, when its sensor is not set)."""
+        forecast (tomorrow, when its sensor is not set).
+
+        `since` is the moment a state-only "left today" figure counts from
+        (OPT-23): `t0` itself when not given, so a span that starts later
+        than now would be spread over what is left of the bell from its own
+        start. Pass now for every span of a plan, and the spans add up to
+        the figure. An hourly split ignores it."""
         if t1 <= t0:
             return 0.0
+        since = t0 if since is None else since
         last = self.tomorrow or self.today
         if t1 > last.day0 + timedelta(days=1, hours=BELL_FROM_H):
             return None
@@ -92,7 +100,7 @@ class Forecast:
             a = max(t0, day.day0)
             b = min(t1, day.day0 + timedelta(days=1))
             if b > a:
-                total += _day_between(day, a, b, t0)
+                total += _day_between(day, a, b, since)
         return total
 
 
@@ -124,8 +132,12 @@ def _day_between(day: Day, a: datetime, b: datetime, now: datetime) -> float:
                 out += kwh * (hi - lo).total_seconds() / (e - s).total_seconds()
         return out
     # State only: `kwh` is what is left from `max(now, day0)` to the day's
-    # end, spread over the bell.
-    h_from = _hours_since(day.day0, max(now, day.day0))
+    # end, spread over the bell. Nothing of it is before that moment.
+    start = max(now, day.day0)
+    a = max(a, start)
+    if b <= a:
+        return 0.0
+    h_from = _hours_since(day.day0, start)
     left = 1.0 - _bell(h_from)
     if left <= 1e-9:
         return 0.0