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/Stats.tsx

@@ -8,6 +8,7 @@ import { notify } from "../lib/notifications";
 import { LS, useAccountPersistedState } from "../lib/storage";
 import Tooltip from "./Tooltip";
 import { Section, SettingRow } from "./ui/form";
+import { useMe } from "../lib/useMe";
 
 const RANGES = [7, 30, 90] as const;
 type StatsTab = "overview" | "system";
@@ -15,7 +16,8 @@ type StatsTab = "overview" | "system";
 // Usage & stats page. "Overview" is per-user (sync status + your own API usage + actions);
 // "System" is the admin-only instance-wide quota dashboard + background-sync control. The
 // per-user content used to live in Settings → Sync; it moved here so Settings stays config-only.
-export default function Stats({ me }: { me: Me }) {
+export default function Stats() {
+  const me = useMe();
   const { t } = useTranslation();
   const isAdmin = me.role === "admin";
   const [tabRaw, setTab] = useAccountPersistedState(LS.statsTab, "overview");