UX-13 P2 review fixes (PR #145, comment 1880)

1. Discard reloads /config/model: after a stale save the page kept the
   new fingerprint with the old values, so Discard + Save overwrote the
   other surface's change without a 409.
2. Removing cards back to one restores the stored inverter shape, so a
   flat site stays flat after add + remove.
3. A choice the page can only keep ("Other time windows") stays offered
   while it is the stored value.
4. A load locks every locked value again.
5. at_zero() needs an accepted 0 W write; before the first one Home says
   "Going to 0 W" (the heartbeat writes every heartbeat_s, so it clears).
6. A field with a unit drops the translation's "(W)" from its label: the
   peak limit read "Peak limit (W)" beside a kW value.
7. A mirrored choice lists the mirrored field's keys, so a search for
   static_profile finds the contract on a fixed-price site.
8. test_settings: a save refused by ui_to_options writes nothing.

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

goodwe_controller/tools/ux13_demo.py

@@ -230,6 +230,8 @@ def controller(state):
     for inv, soc, batt in zip(c.inverters, (62.0, 35.0), (-2500.0, -300.0)):
         inv.soc, inv.batt = soc, (0.0 if state == "shadow" else batt)
         inv.dev_min, inv.dev_max = -5000.0, 5000.0
+        if state != "running":          # 0 W accepted: Home says "Held"
+            inv.last_write = 0.0
     c.grid = -10.0 if state != "shadow" else -2810.0
     c.pv_w = 3900.0
     if state == "alarm":