feat(channels): fix the manager header, scroll only the table rows

Lift the whole subscribed-view header — tabs, sync stats + actions, the
intro, the tag chips and the sync-status chips — into the shell's fixed
band via PageToolbar. Combined with the sticky table header row, only the
channel rows scroll now; everything above them stays put.

The status chips move out of DataTable's controlsLeading into the fixed
chrome (they belong above the header, not in the scrolling controls row).

Note: the DataTable pager (rows-per-page / pagination) stays in the
scroller for now — it rarely shows on the manager (few channels = one
page). The discovery sub-view's chrome is still inline (separate
component, handled in the sweep). Suite 15/15, tsc + knip clean.

frontend/src/components/Channels.tsx

@@ -25,6 +25,7 @@ import { subsColumn } from "./channelColumns";
 import { notify } from "../lib/notifications";
 import Tooltip from "./Tooltip";
 import DataTable, { type Column } from "./DataTable";
+import { PageToolbar } from "./PageShell";
 import ChannelLink from "./ChannelLink";
 import ChannelDiscovery from "./ChannelDiscovery";
 import TagManager from "./TagManager";
@@ -415,8 +416,12 @@ export default function Channels({
 
   return (
     <>
+    {/* The whole manager header — tabs, stats, description, tags, status chips — is fixed chrome:
+        it portals into the shell's fixed band, so only the table rows scroll (under the sticky
+        header row). */}
+    <PageToolbar>
     {tabs}
-    <div className="px-4 pb-4 pt-3 max-w-7xl mx-auto">
+    <div className="px-4 pt-3 pb-2 max-w-7xl mx-auto">
       {/* Per-user sync status + catalog-wide actions on one row (search/tags filtering
           now lives in the table headers). */}
       <div className="flex items-start justify-between gap-4 flex-wrap mb-4">
@@ -535,11 +540,16 @@ export default function Channels({
           {t("channels.tags.manage")}
         </button>
       </div>
-      {tagManagerOpen && (
-        <TagManager onClose={() => setTagManagerOpen(false)} onFocusChannel={onFocusChannel} />
-      )}
+      {/* Sync-status chips — the last band of fixed chrome, right above the table header. */}
+      {statusChips}
+    </div>
+    </PageToolbar>
+    {tagManagerOpen && (
+      <TagManager onClose={() => setTagManagerOpen(false)} onFocusChannel={onFocusChannel} />
+    )}
 
-      {/* Channel table */}
+    <div className="px-4 pb-4 pt-2 max-w-7xl mx-auto">
+      {/* Channel table — only the rows scroll; the header row is sticky (see DataTable). */}
       {channelsQuery.isLoading ? (
         <div className="text-muted py-8">{t("channels.loading")}</div>
       ) : (
@@ -549,7 +559,6 @@ export default function Channels({
           rowKey={(c) => c.id}
           persistKey={accountKey(LS.channelsTable) ?? undefined}
           controlsPosition="top"
-          controlsLeading={statusChips}
           rowClassName={(c) => (c.hidden ? "opacity-60" : "")}
           emptyText={t("channels.empty")}
         />