Group splash animations into four moods (idle/normal/active/heavy) and pick
which group plays based on a 5-min sliding rate of session_pct. Thresholds
sit at 0.10/0.20/0.33 %/min so Heavy fires when usage matches or beats the
5-hour session reset pace. Splash auto-rotates within the current group
every 20s; group recomputes on every BLE poll and the splash re-picks
immediately if it changes mid-display. 4-min minimum window prevents
single-sample bumps after boot from falsely landing in Heavy.
Hermann Björgvin Haraldsson
7ed4710d28