feat(channels): pager into the chip row, Blocked as its own tab

Address manager UAT:
- The DataTable controls row (status chips + pager) now portals into the
  fixed band via a new controlsInBand prop, so it stays put above the
  sticky header instead of scrolling away — and the pager fills the empty
  space next to the status chips, on one row.
- The tab bar is always fixed chrome now (not just on Subscriptions), so
  it doesn't jump when switching tabs; on Subscriptions the stats/intro/
  tags ride with it.
- Blocked channels moves off the bottom of the Subscriptions list into its
  own 'Blocked' tab (with an empty state), alongside Subscriptions and
  Discover.

Verified with a 90-channel test account: everything above the rows stays
fixed while the rows scroll under the sticky header. Suite 15/15, tsc +
knip clean.

frontend/src/App.tsx

@@ -204,7 +204,11 @@ export default function App() {
   // of dumping the user on whatever tab they last left open.
   const [channelsViewRaw, setChannelsView] = useAccountPersistedState(LS.channelsView, "subscribed");
   const channelsView: ChannelsView =
-    channelsViewRaw === "discovery" ? "discovery" : "subscribed";
+    channelsViewRaw === "discovery"
+      ? "discovery"
+      : channelsViewRaw === "blocked"
+        ? "blocked"
+        : "subscribed";
   // Plex module filters (its own left-sidebar filter section) — per-account persisted.
   // The former per-library picker is now a cross-library SCOPE: movie | show | both (unified library).
   // (Reuses the old LS.plexLibrary key; an old stored library-id value falls back to "both".)