feat(settings): turn Appearance into a hub of per-module subpages

Appearance ("Darstellung") stacked every module's view and ordering
settings on one long page. Split it into a hub that lists the modules as
navigable rows, each opening its own /settings/layout/<module> subpage
with a back link — the per-module settings move verbatim, no restyling.
The module routes now redirect to those subpages instead of an in-page
anchor, and the in-app cogs link straight to them.

src/components/illness/illness-view.tsx

@@ -401,7 +401,7 @@ export function IllnessView() {
             className="min-h-11 min-w-11 sm:min-h-9 sm:min-w-9"
           >
             <Link
-              href="/settings/illness"
+              href="/settings/layout/illness"
               aria-label={t("illness.customize")}
               title={t("illness.customize")}
             >