feat(app): the module registry drives the render (S6b DoD)

Replace App's page-render ternary and the three side-rail page conditionals with
a data-driven lookup: components/moduleRegistry maps each page to a prop-free
content component (+ optional side rail + shell fadeTop), and App renders
PAGE_CONTENT[page]/PAGE_RAIL[page] gated by moduleDef(page).gate (an unreachable
gated page falls back to the feed, as the old ternary did). Content modules and
the two rails are now prop-free: they read `me` via the new useMe() hook and
their module-local state from the scoped providers; FeedPage/MessagesPage are the
only wrappers (they wire the global feed scope / meId). App.tsx 796->431 lines,
zero `page===X` chrome conditionals — closes the Platform epic DoD. (Platform S6b.3)

frontend/src/components/SettingsPanel.tsx

@@ -13,6 +13,7 @@ import { type SaveState } from "./ui/DraftSaveBar";
 import { useConfirm } from "./ConfirmProvider";
 import { useWizard } from "./WizardProvider";
 import { usePrefs } from "./PrefsProvider";
+import { useMe } from "../lib/useMe";
 
 // The Settings page edits server-persisted preferences. Each change applies locally for instant
 // preview AND auto-saves (debounced) — no draft, no Save button; a small indicator flashes the
@@ -41,7 +42,8 @@ const TABS: { id: TabId; icon: typeof Monitor }[] = [
 // Settings as a page (Design B): rendered in the main content area, not an overlay. It keeps
 // the frosted `.glass` surface so it still refracts the ambient backdrop. The page title is
 // shown by the Header; the tab rail stays as in-page sub-navigation.
-export default function SettingsPanel({ me }: { me: Me }) {
+export default function SettingsPanel() {
+  const me = useMe();
   const { t } = useTranslation();
   // The editable prefs (theme/perf/hints/notifications + save state) live in PrefsProvider.
   const prefs = usePrefs();