SAFETY-135 round 2: the first guard stop in a period may restart once; tests and docs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bdqr7PiaHcBnzPituu2yTC

goodwe_controller/app/main.py

@@ -529,7 +529,7 @@ class Controller(InputsMixin, WritesMixin, TradeMixin, CycleMixin, AlarmsMixin,
         self._mode_trade_was = False
         self._charge_blocked_q = None
         self._charge_gap_q = None       # OPT-15: an unmeasured stop's quarter
-        self._charge_young_q = None     # SAFETY-135: a young stop's quarter
+        self._charge_stop = None        # SAFETY-135: (quarter, t) first stop
         self._gave = collections.deque()  # SAFETY-135: (t, W given), GAVE_S
         self._ref_cheap = None
         # OPT-15: a run edge the loop holds at E: (E, step sign, until, the