refactor(header): remove the ModuleName module-switcher pill

The user no longer wants the header's "FEED" pill (module label + accent dot + ◀/▶ module-step
arrows). Drop it everywhere — the header now starts with the module's SearchBar; module switching
stays on the nav rail.

Deletes ModuleName.tsx, the now-unused stepModule() in lib/modules, and the Header's
module-order/label/setPage plumbing that only fed it.

frontend/src/lib/modules.ts

@@ -145,15 +145,3 @@ export const SYSTEM_PAGES: readonly Page[] = MODULES.filter((m) => m.system).map
 export function moduleOrder(me: Me): Page[] {
   return MODULES.filter((m) => !m.gate || m.gate(me)).map((m) => m.id);
 }
-
-// Step to the next/previous module cyclically (wraps at both ends). `dir` = +1 forward, -1 back.
-// If the current page isn't a primary module (e.g. Settings), forward lands on the first module
-// and back on the last.
-export function stepModule(me: Me, current: Page, dir: 1 | -1): Page {
-  const order = moduleOrder(me);
-  if (order.length === 0) return current;
-  const i = order.indexOf(current);
-  // order is non-empty (guarded above) and every index below is in-bounds, so none are undefined.
-  if (i === -1) return dir === 1 ? order[0]! : order[order.length - 1]!;
-  return order[(i + dir + order.length) % order.length]!;
-}