SAFETY-95: a maintenance drain that ends hands back smoothly (N>=2)

When a battery's drain ended (done, Off, timeout, abort, stale link,
refusal), its drain floor stayed in the site target and landed on the
others: B 0 -> +1600 W in one cycle at a 1200 W house, exporting; under a
solar surplus B gave into the export.

Now, on that cycle, the loop starts from what the others stood at plus the
battery's new command, raised to the house's own point when the house needs
more (never above last cycle's start). While the battery settles, the loop
counts the batteries at its start instead of chasing the drain's tail on
the meter. Then one slew step a cycle. N=1 is unchanged.

test_safety95.py; DECISIONS/SAFETY-95-drain-end.md; one DOCS line.
test_modes.py: opt11 n2_maint re-pinned on purpose (its drain ends by a
refusal at 1655 s; B now stays at the house's 1420 W instead of 2500 W).

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

goodwe_controller/DOCS.md

@@ -1702,6 +1702,9 @@ When a charge ends, the other batteries take over one slew step a cycle,
 and none starts charging from the grid (SAFETY-93).
 When a battery's link drops, the others take over one slew step a cycle,
 and control does not stall on the dropped battery's power (SAFETY-96).
+When a drain ends (done, Off, timeout, abort, link, refusal), the others
+cover the house at once but never take over its export; from there control
+moves one slew step a cycle (SAFETY-95).
 
 #### Capacity-tariff exposure of the grid-following loop