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/FilterSelect.tsx

@@ -13,7 +13,6 @@ import { SURFACE } from "./surfaces";
 // Built on the same AnchoredPopover platform as ActionMenu/Combobox (arrows/typeahead/Escape/anchor-flip);
 // reusable anywhere a small, known set of options currently renders as a chip group. See FilterSelect.dom.test.
 
-/** @internal exported for FilterSelect.dom.test.tsx */
 export interface FilterSelectOption {
   value: string;
   label: string;

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;
 

frontend/src/components/ui/readAhead.ts

@@ -8,16 +8,12 @@
 //   - ceiling MAX_LOOKAHEAD_ROWS: a tall window renders many rows, and an uncapped lookahead would
 //     eagerly prefetch several pages on every mount / filter change — wasted work on the app's
 //     heaviest query (the feed). The cap bounds that while still buffering a couple of screens ahead.
-/** @internal exported for readAhead.test.ts */
 export const PREFETCH_ROWS = 4;
-/** @internal exported for readAhead.test.ts */
 export const PREFETCH_VIEWPORTS = 2;
-/** @internal exported for readAhead.test.ts */
 export const MAX_LOOKAHEAD_ROWS = 40;
 
 /** How many rows ahead of the last rendered row to keep buffered, for a viewport rendering
  *  `renderedRows` rows. Clamped to [PREFETCH_ROWS, MAX_LOOKAHEAD_ROWS]. */
-/** @internal exported for readAhead.test.ts */
 export function readAheadLookahead(renderedRows: number): number {
   return Math.min(MAX_LOOKAHEAD_ROWS, Math.max(PREFETCH_ROWS, renderedRows * PREFETCH_VIEWPORTS));
 }

frontend/src/components/ui/scrollFold.ts

@@ -10,7 +10,6 @@ import { CONTENT_ID } from "./landmarks";
 //    back (`room - saving > FOLD_AT`): a page barely taller than the window would otherwise fold, lose its
 //    scroll, land at the top, unfold, and so on, with every wheel tick;
 //  - unfold only at the very top, not at the fold point: between the two the header keeps whatever it was.
-/** @internal exported for scrollFold.test.ts */
 export const FOLD_AT = 32;
 
 interface ScrollPosition {
@@ -21,7 +20,6 @@ interface ScrollPosition {
 }
 
 // `saving` = the height the header gives back when it folds (measured while it is unfolded).
-/** @internal exported for scrollFold.test.ts */
 export function nextFolded(
   folded: boolean,
   { top, room }: ScrollPosition,