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/Playlists.tsx

@@ -31,7 +31,7 @@ import {
   X,
   Youtube,
 } from "lucide-react";
-import { api, type Me, type Video } from "../lib/api";
+import { api, type Video } from "../lib/api";
 import { formatDuration } from "../lib/format";
 import { notify } from "../lib/notifications";
 import { notifyYouTubeActionError } from "../lib/youtubeErrors";
@@ -41,6 +41,7 @@ import UndoToolbar from "./UndoToolbar";
 import { PageToolbar } from "./PageShell";
 import { useConfirm } from "./ConfirmProvider";
 import { usePlaylists, usePlaylistsActions } from "./PlaylistsProvider";
+import { useMe } from "../lib/useMe";
 
 type SortKey = "manual" | "title" | "duration" | "channel";
 type SortDir = "asc" | "desc";
@@ -179,7 +180,8 @@ function Row({
   );
 }
 
-export default function Playlists({ me }: { me: Me }) {
+export default function Playlists() {
+  const me = useMe();
   const canWrite = me.can_write;
   // The selected playlist lives in PlaylistsProvider, shared with the PlaylistsRail (which owns the
   // list + its rail controls). This detail pane reacts to the selection.