Follow-up to the cherry-picked #41909/#92696 + #39760 + #97970 cluster:
- single field-key namespace (display.status_bar.fields) instead of the
second tui_statusbar_fields list; cache_hit/latency/tps/stash/battery/
title join the existing key set
- cache-hit % prefers the baseline-delta regime (resets on model switch
and compression) and hides on zero cache reads instead of alarming 0%
- latency/tps segments added to the styled fragment renderer too
- docs updated in website/docs/user-guide/configuration.md
- 7 new tests: rolling latency/t/s, NaN/negative guard, field filtering,
baseline resets, title badge gating
9e017428ba