MAINT-13 round 2: gate open when nothing holds the charge back; safety93 scenario restored

- gate_open is true with no price gate set up, in a cheap window, or while the
  pack is taking charge; the stall rule and timeout now work on a no-tariff site.
- reset the save timer on a phase change; exact 5 min gap-cap test.
- test_safety93: original timeout scenario kept (B finished) plus a case where a
  due B takes the slot after A's failure.

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

goodwe_controller/app/maintenance.py

@@ -375,6 +375,7 @@ class Maintenance:
 
     def _enter(self, phase: str, now: datetime, events: list, msg: str) -> None:
         self._trk = None
+        self._trk_saved = None
         if self.store.get("charge_track") is not None:
             self.store.set("charge_track", None)
         self.store.set("phase", phase)