MAINT-14: maintenance with no SoC reading: charge times out, drain holds at 0 W

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

goodwe_controller/test_maintenance.py

@@ -122,7 +122,8 @@ m = Maintenance(cfg, FakeStore())
 m.force_start(t0)
 r = m.tick(t0 + timedelta(minutes=5), soc=None)
 check("no SoC: holds the phase rather than guessing", r.phase == DRAIN)
-check("no SoC: still commands the drain rate", r.setpoint_w == 2500)
+check("no SoC: MAINT-14 the drain holds at 0 W, never discharges",
+      r.owns_setpoint and r.setpoint_w == 0.0)
 
 m = Maintenance(cfg, FakeStore())
 m.store.set("phase", "banana")