SAFETY-78: maintenance drain at N=2 no longer stalls

At two inverters the drain pins its pack and the site target is split
around the pin. Below the pin the other pack had to charge, the allocator
refused the opposite directions, and the site sat at 0 W with an ARBITER
line every cycle (house below or above the drain rate, or a grid charge).

main.py now files a site limit `drain` (lo = what the pin places, at
P_MAINTENANCE) at N>=2 while a pack drains, so the other pack only adds
power in the same direction. A drain that cannot give power waits with
one log line. With battery modes on, no grid charge while a pack drains,
and the other battery's card says why. N=1 is byte-identical.

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

goodwe_controller/app/ui_text/en.json

@@ -327,6 +327,7 @@
       "leftover_alone": "No Solar first battery is on, so it gets solar first.",
       "covers_house": "It gives power to cover the house.",
       "other_refuses": "{name} refuses to give power, so this battery takes over.",
+      "other_cycle": "{name} is emptying for its monthly cycle. This one does not charge.",
       "grid_charge": "Prices are low, so it charges from the grid.",
       "rests_charge": "Another battery charges from the grid, so it rests.",
       "selling": "Prices are high, so it sells to the grid.",

goodwe_controller/app/ui_text/nl.json

@@ -269,6 +269,7 @@
       "leftover_alone": "Geen batterij met Eerst zonne-energie staat aan, dus zij krijgt eerst zonne-energie.",
       "covers_house": "Ze levert stroom om het huis te dekken.",
       "other_refuses": "{name} weigert te leveren, dus deze batterij neemt het over.",
+      "other_cycle": "{name} loopt leeg voor haar maandelijkse cyclus. Deze laadt niet.",
       "grid_charge": "De prijs is laag, dus ze laadt van het net.",
       "rests_charge": "Een andere batterij laadt van het net, dus deze rust.",
       "selling": "De prijs is hoog, dus ze verkoopt aan het net.",