refactor(modules): consolidate nav into a module registry

Extend lib/modules.ts into an ordered ModuleDef registry (id/label/icon/
system/badge/gate) as the single source for the nav rail and the header
stepper. Absorb NavSidebar's per-page ICON map; derive moduleOrder /
moduleLabelKey / SYSTEM_PAGES from the one array. Render still on the App
ternary — this is the scaffold S6b.3 will drive from. (Platform S6b.1)

frontend/src/components/NavSidebar.tsx

@@ -4,32 +4,21 @@ import { useTranslation } from "react-i18next";
 import { useQuery } from "@tanstack/react-query";
 import { useNavigation, useNavigationActions } from "./NavigationProvider";
 import {
-  Activity,
-  BarChart3,
-  Bell,
-  Clapperboard,
-  Download,
-  Home,
   Info,
-  ListVideo,
   LogOut,
-  MessageSquare,
   Pin,
   PinOff,
-  ScrollText,
   Settings,
   Shield,
-  SlidersHorizontal,
-  Users,
-  Tv,
   UserPlus,
+  type LucideIcon,
 } from "lucide-react";
 import { api, clearActiveAccount, setActiveAccount, type Me } from "../lib/api";
 import * as e2ee from "../lib/e2ee";
 import { useLiveQuery } from "../lib/useLiveQuery";
 import { getUnreadCount, subscribe } from "../lib/notifications";
 import type { Page } from "../lib/urlState";
-import { moduleLabelKey, moduleOrder, SYSTEM_PAGES } from "../lib/modules";
+import { moduleDef, moduleLabelKey, moduleOrder, SYSTEM_PAGES } from "../lib/modules";
 import { useScrollFade } from "../lib/useScrollFade";
 import { useHoverFocusWithin } from "../lib/useHoverFocusWithin";
 import { type LangCode } from "../i18n";
@@ -177,34 +166,18 @@ export default function NavSidebar({
   // also used by the side panels) so a high-zoom overflow scrolls without a scrollbar.
   const listFade = useScrollFade();
 
-  type NavItem = { page: Page; icon: typeof Home; label: string; badge?: number };
-  // Per-page presentation (icon/label/badge). WHICH pages appear and in what order comes from the
-  // shared moduleOrder(me) — the same source the header's ◀/▶ stepper uses — so the two never drift
-  // and a new/gated module updates both at once. Badges live here (nav-only concern).
-  // Icon + badge per page; the label comes from the shared moduleLabelKey so the rail and the
-  // header's ModuleName pill always read the same name.
-  const ICON: Record<Page, typeof Home> = {
-    feed: Home,
-    channels: Tv,
-    playlists: ListVideo,
-    plex: Clapperboard,
-    notifications: Bell,
-    messages: MessageSquare,
-    downloads: Download,
-    stats: BarChart3,
-    scheduler: Activity,
-    config: SlidersHorizontal,
-    users: Users,
-    audit: ScrollText,
-    settings: Settings,
-  };
+  type NavItem = { page: Page; icon: LucideIcon; label: string; badge?: number };
+  // Per-page presentation (icon/label/badge). WHICH pages appear and in what order — and each
+  // module's icon + label — come from the shared module registry (the same source the header's
+  // ◀/▶ stepper uses), so the two never drift and a new/gated module updates both at once. The
+  // badge NUMBERS are the only nav-only concern (they need the live polling queries above).
   const BADGE: Partial<Record<Page, number>> = {
     notifications: unread,
     messages: msgUnread,
     downloads: dlActive,
   };
   const META = (p: Page): Omit<NavItem, "page"> => ({
-    icon: ICON[p],
+    icon: moduleDef(p).icon,
     label: t(moduleLabelKey[p]),
     badge: BADGE[p],
   });