Review follow-ups on the tier-shift fix. The table moves to a module-level
RELATIVE_UNITS: it is constant, so rebuilding it per call was pure garbage on
a path that runs once per rendered timestamp across a virtualized feed.
Its ascending order is load-bearing and was unstated — sorting it largest-first
would make every timestamp under a year read "just now", silently, the same
shape as the bug this branch fixes. It is now documented and asserted, and the
suite derives its tier coverage and translation checks from the table itself
rather than from its own case list, so a new tier cannot slip in uncovered.
The audit log read the empty string for an unreadable date as a value and
rendered a blank cell; it now uses the `|| "—"` idiom the channel table
already uses, so missing and unreadable dates look alike.
The repo had no unit-test runner, so this adds the minimum: vitest (3.x, as
4.x needs Vite 6), a node-env config deliberately separate from vite.config.ts
so the production build never loads it, npm test / test:watch, and a knip
entry so the config and specs are not reported unused. Browser flows stay in
e2e/ under Playwright.
The suite samples every tier at its exact opening second as well as inside it,
and stubs i18n so each assertion lands on the key rather than the copy. An
interior-only suite still passes when the range comparison flips to <=, which
is how the tier shift went unnoticed for so long.
Locks the five flows the refactor must not break (feed, channel, player,
settings, nav) so later sprints can prove they changed nothing. Adds a thin
data-testid layer and a dedicated seeded non-demo account; the suite runs on
the baked :8080 stack (authoritative) or :5173. No product-behaviour change.
peter