build(frontend)!: knip drops --production; plain knip stays

The production pass (7ed2ac4e, E32) asked "is this export used by what
ships?". No real hit: its only findings were 37 exports a test imports,
answered with 36 `@internal` JSDoc tags (E34 S2) — test-only exports, not
defects. Since then it has only ever asked for another tag. The tags go
with it (36, no longer read by anything), and so do the production-only
`!…!` exclusions in knip.jsonc and their register rows. Plain knip (unused
files, exports and dependencies) keeps running in the gate.

frontend/src/components/ui/progressiveRows.ts

@@ -12,7 +12,6 @@ import { startTransition, useEffect, useState } from "react";
 //
 // Not virtualization: every row still ends up in the DOM, so browser find, keyboard nav past the screen,
 // and the Back focus/scroll restore (which wait for the list to grow) keep working as they did.
-/** @internal exported for DataTable.progressive.dom.test.tsx */
 export const FIRST_ROWS = 30;
 const STEP_ROWS = 40;