SAFETY-84: maintenance charge at N=2 no longer stalls

At N>=2 a cheap-window maintenance charge files a site `hi` (`charge`,
P_MAINT_SHAPE) equal to what the charging pack's own `hi` places, so the
other pack never has to give against it. The charge is sized to the
quarter's headroom under the peak aim so it yields to the peak guard, and
to 0 W under a site safety stop. N=1 byte-identical (safety84_identity).

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

goodwe_controller/app/allocator.py

@@ -354,6 +354,11 @@ def pin_w(b):
     return float(pv) if lo > hi else float(_clamp_int(round(float(pv)), lo, hi))
 
 
+def hi_w(b):
+    """A unit's upper hard limit as `plan()` narrows it to whole W (SAFETY-84)."""
+    return float(_int_envelope(b)[1])
+
+
 def loop_bound(bounds, live=None):
     """OPT-11. `(lo, hi)`: what the units can place when the LOOP decides.