fix(inverter): stop holds commanding a grid charge on charge-target inverters

[romain-intel]

Predbat holds the battery by writing a reserve one percent above the current SoC, which stops discharge on inverters that defend the reserve passively. The Powerwall instead treats the reserve as a level to charge towards, so every hold - freeze charge, Hold for car, Hold for iBoost - was a grid import request.

Adds a reserve_is_charge_target inverter capability (TESLA only; every other inverter definition is unchanged and reads the default via .get). When set:

• hold_reserve_percent() holds exactly at the level instead of one above it
• adjust_reserve() refuses to write a reserve above the current SoC at all, so the bug class is impossible regardless of what a caller asks for
• freeze targets use a new calc_percent_limit_floor(), because rounding to nearest turns a 61.6% SoC into a 62% target - the same off-by-one by another route

Also fixes a related divergence in the Teslemetry scheduler emulator, which decided device commands from its own Fleet live_status poll rather than the SoC Predbat planned against (different on a site with local monitoring), and could replay a persisted idle reserve above SoC after a restart.

Refs #4424, #4432, #4440