fix(config): raise charge_low_power_margin max from 30 to 60 minutes (#4347)

find_charge_rate (utils.py) handles a margin exceeding the charge window
safely (falls back to max-rate charging), so there's no correctness reason
for the 30-minute cap - it's been that low since the setting was added.
Became newly enforceable after 013558e started clamping apps.yaml
overrides to their declared min/max, which is what surfaced this as a
regression for anyone who'd previously relied on an unclamped apps.yaml
value above 30. Fixes #4320.

Author: chalfontchubby

apps/predbat/config.py

@@ -875,7 +875,7 @@
         "friendly_name": "Low power mode margin",
         "type": "input_number",
         "min": 0,
-        "max": 30,
+        "max": 60,
         "step": 5,
         "unit": "minutes",
         "icon": "mdi:seatbelt",