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/app/main.py

@@ -3472,7 +3472,9 @@ class Controller:
             # power: not used, as if the option were empty.
             st = await self.hass.state(o["peak_forecast_entity"])
             self.peak_fc, _why = pv_read.watts(st)
-            self._peak_fc_unit_log(pv_read.unit_fault(st))
+            # A missing reading leaves the unit-fault state as it was.
+            if pv_read.has_reading(st):
+                self._peak_fc_unit_log(pv_read.unit_fault(st))
         else:
             self.peak_fc = None
             self._peak_fc_fault = None