Design doc capturing the architectural pattern behind the perf-card
flicker (every innerHTML rewrite tears down the subtree, restarting
CSS animations / dropping focus / wasting layout) and the two
drivers — poll timers and server:* push events. Inventories every
remaining latent site in perf-charts.ts / dashboard.ts /
entity-events.ts / game-integration.ts, walks the decision ladder
from a setInnerHtmlIfChanged helper through hand-rolled cell
components to a Lit migration, and lands on Lit for polling-heavy
modules with entity-events.ts tab reconciliation sequenced ahead of
the dashboard cards because of its higher blast radius.
Planning artifact only — no implementation here.
