OPT-11 P3: price runs per battery

Cheap and expensive hours as runs of consecutive firm price slots
(priceruns.py); each battery's role per tick from its mode (modetrade.py):
grid charging for Leftover solar / Cheap hours only, never Solar first;
holding for the expensive runs; selling per battery (pack_sell) above the
spread and the floor. The site trade is sized inside the modes (loop bound)
and the peak guard's headroom; a run edge reseeds the loop. Cheap hours only
and selling are enabled on the Batteries screen and in the HA select
(appended). The site Why row no longer says "held back" when the peak limit
pushes power up (F2). Modes off: byte-identical to 7a00f12 on the trade path.

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

goodwe_controller/app/mqtt.py

@@ -453,7 +453,8 @@ def discovery_payloads(units=(), omit=(), include=(), modes=()) -> list:
 #
 # The select's options are these labels, in `packmode.MODES` order. A new mode
 # (P3) is a new entry here and a new option at the end; no id changes.
-MODE_LABELS = {"solar_first": "Solar first", "leftover_solar": "Leftover solar"}
+MODE_LABELS = {"solar_first": "Solar first", "leftover_solar": "Leftover solar",
+               "cheap_hours": "Cheap hours only"}         # OPT-11 P3
 USE_ON, USE_OFF = "ON", "OFF"
 # A longer command payload is refused before it is decoded.
 MAX_COMMAND_BYTES = 64