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/pv.py

@@ -126,19 +126,26 @@ def watts(state: dict | None) -> tuple:
     return value * WATTS_PER[unit], unit
 
 
-def unit_fault(state: dict | None):
-    """SAFETY-118. `None` unless `state` holds a number whose unit cannot be
-    read in watts, then that unit (`""` for none). A missing, unavailable or
-    non-numeric state is a missing reading, not a unit fault, so it is `None`.
-    """
+def has_reading(state: dict | None) -> bool:
+    """SAFETY-118. True when `state` holds a number, so its unit can be judged.
+    A missing, unavailable, unknown or non-numeric state is a missing reading."""
     if state is None:
-        return None
+        return False
     raw = str(state.get("state", "")).strip()
     if raw.lower() in BAD_STATES:
-        return None
+        return False
     try:
         float(raw)
     except ValueError:
+        return False
+    return True
+
+
+def unit_fault(state: dict | None):
+    """SAFETY-118. `None` unless `state` holds a number whose unit cannot be
+    read in watts, then that unit (`""` for none). `None` also means a missing
+    reading: use `has_reading()` to tell it from a good unit."""
+    if not has_reading(state):
         return None
     unit = str((state.get("attributes") or {}).get(UNIT_KEY) or "").strip()
     return None if unit in WATTS_PER else unit