docs(sigenergy): fix rate automation sensor names, re-apply mode on restart, stop zeroing import limit in freeze

[chalfontchubby]

🤖 Written and posted by Claude (Claude Code) on behalf of @chalfontchubby. Draft while the changes are dogfooded on a live Sigenergy system.

Summary

Fixes the Sigenergy Sigenstor setup instructions reported in #5459, plus three problems found while checking them against a live system:

1. The rate automations reference sensors that don't exist. They now use the plant-level sensor.sigen_plant_ess_rated_charging_power / ..._discharging_power, as the SigEnergy Sigenstor setup documentation #5459 reporter found and as the template's battery_rate_max already does.
2. A Home Assistant restart can leave the battery exporting past its target. The mode automation now re-applies the mode after a restart.
3. Freeze modes no longer set the grid import limit to 0 (Sigenergy template locks grid import to 0 even when EV is charging #4911).
4. Remote EMS has to be on, which the page never said. There's also an optional watchdog that turns it back on.

As agreed with @gcoan on #5459, this PR is the write-up of the Sigenergy section: it brings the docs in line with the setup running on the live system.

Detail

Rate automations (#5459). sensor.sigen_inverter_ess_rated_charging_power (inverter prefix with "-ing" suffix) matches neither of the integration's spellings, so the | float raised float got invalid input 'unknown'.

• The automations now cap against the plant-level sensors, which match the plant-level limits they write.
• They skip the write if the rate input isn't a number, rather than writing a 0 kW limit.
• An unavailable rated-power sensor means no cap, rather than 0.
• The renamed-entities note is rewritten around the plant/inverter split.
• A new note warns that renaming charge_rate/discharge_rate in apps.yaml without changing the automations stops them firing, with nothing reported. That happened on the live system (also flagged by tdbegley28 on Sigenergy template locks grid import to 0 even when EV is charging #4911): the plant sat at a fixed 5.5 kW for months and never received Predbat's rate-0 holds.

Restarts. input_select.predbat_requested_mode had initial: "Demand", so a restart reset it without a state change and the mode automation never fired. On the live system a restart at 18:59, at the end of an 18:30–19:00 force export, left the plant on Command Discharging. By then Predbat wanted Demand, saw Demand, and wrote nothing, so the battery exported at 5.5 kW from 33% to 22% until it was corrected by hand. The fix:

• initial: is dropped from the three helpers, so HA restores their state.
• The mode automation also triggers on homeassistant: start and on Remote EMS going from off to on.
• It waits for the select and the SoC sensor before writing.
• The Freeze Charging pin now falls back to 0, not 100, if SoC can't be read. With the new triggers, a 100 fallback could pin the discharge cut-off at 99.75% and trigger the forced-import firmware bug this section documents.

Import limit in freeze modes (#4911). The charge and discharge cut-offs enforce the freeze; the 0 kW import limit was left over from before #4392. It contradicts Freeze Charging's own definition (house load beyond solar comes from the grid), and it stalls Sigenergy EVAC/EVDC chargers behind the plant CT. Existing users are told to reset it once after updating.

Other changes

• The enable list now names sensor.sigen_plant_daily_load_consumption, which is what the template uses.
• The "Remote EMS must be on" note says the cut-off and limit numbers are still obeyed while it's off, which can make a setup look partly working.
• The optional watchdog checks every 30 minutes. It has a commented-out Axle condition, so it doesn't take control back from Axle in the middle of an event.

Testing

Documentation only. Every YAML block in the section parses, and the key templates render as expected with sample states, including unknown/unavailable inputs. Pre-commit passes.

The same automations are running on a live Sigenergy system (SigenStor, TypQxQ Sigenergy-Local-Modbus):

• The freeze modes without the 0 import limit since 9 Sep.
• Everything else since 9 Oct.

Not yet exercised live: the new restart trigger (it needs another HA restart in a non-Demand mode) and the first rate-0 hold reaching the inverter. I'll update here once both have been seen.

Closes #5459
Closes #4911

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