SAFETY-118: a missing peak forecast reading keeps the unit-fault state

A missing reading (unavailable, unknown, failed read, non-numeric) no longer
clears the fault: no false 'used again' INFO, no repeated WARNING, the status
row stays. Adds pv.has_reading(). DECISIONS wording fixed; tests added.

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

goodwe_controller/DECISIONS/SAFETY-118-peak-forecast-unit.md

@@ -4,8 +4,8 @@
 
 `peak_forecast_entity` was read as a bare number, and anything under 50 was
 multiplied by 1000 ("accept kW or W"). A W sensor reading 17 to 45 W, which a
-real site did 430 times in one morning, was taken as 17 to 45 kW. The validator
-also called a kW sensor wrong, which was false for this entity.
+real site did 430 times in one morning, would be taken as 17 to 45 kW. The
+validator also called a kW sensor wrong, which was false for this entity.
 
 Decision: the size rule is gone. The entity is read through `pv.watts()`, the
 same unit table and reader as the solar entities, so W, kW, MW and the rest