OPT-27 round 3: a kept figure is at most 12 h old; DST-safe midnight bound; pruning test

F1: the evening rule has an age limit (KEPT_MAX_AGE_S).
F2: the evening bound is the next local midnight (_bounds), right on 25 h and 23 h days.
F5: test that old days are dropped from the stored hold.

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

goodwe_controller/DOCS.md

@@ -557,7 +557,7 @@ With battery modes on, these choices replace the *Charging and selling on price*
 - The plan is checked every 15 minutes. A planned level moves only by 1 kWh or 10 %, so a wobbling forecast does not flip it.
 - No forecast, one older than 3 hours or from before midnight, or no house use yet: *Leftover solar* takes solar only and *Cheap hours only* fills to the top level. The Batteries screen says so.
 - A battery needs its capacity (`inverters.capacity_kwh`) for a plan.
-- **At night.** Some forecasts stop updating in the evening (Forecast.Solar does). The add-on keeps the last reading of each sensor and uses it for that night's plan: from 20:00 until 03:00, or until a newer reading comes. A sensor that is missing for up to 3 hours is covered the same way. A figure is never used for another day, and never older than that night. The Batteries screen says "Solar forecast read 17:05, kept for tonight." With no reading all day, the night run still needs the wider gap.
+- **At night.** Some forecasts stop updating in the evening (Forecast.Solar does). The add-on keeps the last reading of each sensor and uses it for that night's plan: from 20:00 until 03:00, or until a newer reading comes. A sensor that is missing for up to 3 hours is covered the same way. A figure is never used for another day, and never when it is more than 12 hours old. The Batteries screen says "Solar forecast read 17:05, kept for tonight." With no reading all day, the night run still needs the wider gap.
 
 **What always comes first.**
 - The peak limit, the safety stops and the monthly cycle come before a battery's mode.