Arm (or replace) a boost

Boost charges NOW - an Active claim at priority 200 (above Divert and the Scheduler, below Manual and Limit) - until the target is reached, then releases so the previous controller resumes. Re-POSTing while a boost is active replaces it with a fresh activation snapshot. Time values clamp to 604800 seconds (7 days). Energy value is a Wh delta from the moment of activation; soc/range values are absolute targets and require a vehicle data source (422 otherwise). A soc/range target that is ALREADY met arms as a no-op: 201, no claim is taken, and GET /boost still returns {}. The MQTT <base>/boost event topic publishes the boolean boost + boost_version on every change; boost_reason ("reached", "cancelled" or "replaced") appears only on end events (boost false) and never on an active one, so a replace emits the end event first and then the fresh arm event. The retained <base>/boost state topic carries this same serialized object ({} when idle) - the retained remaining is a snapshot at arm/end, not a live countdown.