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/DOCS.md

@@ -530,8 +530,8 @@ Off by default. Turn it on, restart the add-on, and the Batteries screen (and Se
 - **On or off.** Off asks the battery for 0 W and starts no monthly cycle on it. A cycle that is running stops, and the add-on log says so. The peak limit may still use it, but only for what the other batteries cannot cover.
 - **Mode.**
   - *Solar first* charges from spare solar before the other batteries and covers the house at any hour. It never charges from the grid and never sells.
-  - *Leftover solar* charges from the solar the others cannot take. With a solar forecast it may also charge from the grid, but only what the sun will not give (see below). It saves its power for the expensive hours and covers the house then.
-  - *Cheap hours only* charges from the grid in the cheapest hours, saves its power for the expensive hours and covers the house then.
+  - *Leftover solar* charges from the solar the others cannot take. With a solar forecast it may also charge from the grid, but it buys only what the sun will not give in the expensive hours (see below). It saves its power for those hours and covers the house then.
+  - *Cheap hours only* fills up from the grid in the cheapest hours, saves its power for the expensive hours and covers the house then. It does not look at the forecast.
 - **Selling** is off until it can be judged on the price the grid pays (owner decision 2026-09-29, option A).
 
 With battery modes on, these choices replace the *Charging and selling on price* switch (`arbitrage_enabled`); that switch is only read with modes off.
@@ -548,7 +548,9 @@ With battery modes on, these choices replace the *Charging and selling on price*
 - If one of them has no reading, is stale or is not in an energy unit, that day's forecast is not used at all. A part of the sun is not counted as all of it. The status page names the source by its place in the list.
 - The hourly shape is kept only if every sensor has one. Otherwise the total is spread over the day as for Forecast.Solar.
 - Before each cheap run the add-on asks: will the sun fill the batteries before the expensive hours? It counts on `solar_trust_pct` of the forecast (70 %), less what the house uses. Solar first batteries get that sun first.
-- *Leftover solar* then charges from the grid only the shortfall: what the house will draw from it in the expensive hours, less its share of the sun. Not up to the top level.
+- *Leftover solar* then charges from the grid only the shortfall: for each expensive hour, what the house uses less the sun counted for that hour (never below 0), added up over all the expensive hours, early morning and evening. With a day and night tariff that is 07:00 to 22:00. Not up to the top level.
+- All *Leftover solar* batteries hold that shortfall together, shared by their size. A battery that reaches the top level passes the rest to the others. If all of them together cannot hold it, they all fill to the top level and the grid covers the rest in the expensive hours. The Batteries screen says so. The sun before the expensive hours still fills first, and is taken off what is bought.
+- A forecast that gives only one figure for the day (Forecast.Solar) is spread over the hours from now, so the hours add up to that figure.
 - *Cheap hours only* ignores the forecast and fills to the top level.
 - *Solar first* never charges from the grid.
 - The house use is the add-on's own measurement (grid + battery power) per hour, over the last 7 days. It needs one day of it before the first plan.