feat(managers): actions-first discovery table, tabs in the back chain, pager scrolls to top

UAT round 4:
- Discovery table: move Actions to the first column, mirroring the Subscriptions
  table (where it sits right after Prio) so both tabs' actions line up.
- The manager's tabs now ride in history.state (`_chTab`), the same way the channel
  page (`_chan`) and the live search (`_yt`) already do — so Back steps back through
  the tabs you visited before it leaves the module. Arriving from elsewhere stamps
  the entry setPage pushed (one navigation never costs two Back presses).
- Turning a page now scrolls the list back to its top (both the tables and the card
  grid, since they share Pager) — landing mid-list in an unseen page is disorienting.

frontend/src/components/ChannelDiscovery.tsx

@@ -97,6 +97,34 @@ export default function ChannelDiscovery({
   );
 
   const columns: Column<DiscoveredChannel>[] = [
+    // Actions first, mirroring the Subscriptions table (where it sits right after Prio) so the two
+    // tabs' action clusters line up in the same place.
+    {
+      key: "actions",
+      header: t("channels.cols.actions"),
+      align: "left",
+      nowrap: true,
+      width: "120px",
+      cardLabel: false,
+      render: (c) => (
+        <Tooltip
+          hint={
+            canWrite
+              ? t("channels.discovery.subscribeHint")
+              : t("channels.discovery.needWriteHint")
+          }
+        >
+          <button
+            onClick={() => onSubscribe(c)}
+            disabled={!canWrite || subscribe.isPending}
+            className="glass-card glass-hover inline-flex items-center gap-1.5 px-2.5 py-1.5 rounded-lg text-xs disabled:opacity-50 transition"
+          >
+            <UserPlus className="w-3.5 h-3.5" />
+            {t("channels.discovery.subscribe")}
+          </button>
+        </Tooltip>
+      ),
+    },
     {
       key: "channel",
       header: t("channels.cols.channel"),
@@ -156,32 +184,6 @@ export default function ChannelDiscovery({
         </Tooltip>
       ),
     },
-    {
-      key: "actions",
-      header: t("channels.cols.actions"),
-      align: "right",
-      nowrap: true,
-      width: "120px",
-      cardLabel: false,
-      render: (c) => (
-        <Tooltip
-          hint={
-            canWrite
-              ? t("channels.discovery.subscribeHint")
-              : t("channels.discovery.needWriteHint")
-          }
-        >
-          <button
-            onClick={() => onSubscribe(c)}
-            disabled={!canWrite || subscribe.isPending}
-            className="glass-card glass-hover inline-flex items-center gap-1.5 px-2.5 py-1.5 rounded-lg text-xs disabled:opacity-50 transition"
-          >
-            <UserPlus className="w-3.5 h-3.5" />
-            {t("channels.discovery.subscribe")}
-          </button>
-        </Tooltip>
-      ),
-    },
   ];
 
   // Card layout paginates like the table (slice the sorted rows; the Pager reports changes).

frontend/src/components/ChannelsProvider.tsx

@@ -120,9 +120,19 @@ export function ChannelsProvider({ children }: { children: ReactNode }) {
     setStatusFilterState(f);
     setAccountRaw(LS.channelFilter, f);
   }, []);
+  // The active tab rides in history.state (`_chTab`), the same way the channel page (`_chan`) and the
+  // live YouTube search (`_yt`) do — so Back steps back through the tabs you actually visited instead
+  // of jumping straight out to the previous module.
   const setView = useCallback((v: ChannelsView) => {
     setViewState(v);
     setAccountRaw(LS.channelsView, v);
+    const st = window.history.state || {};
+    // Only own an entry while the manager is already on screen. Arriving from elsewhere
+    // (focusChannel / goToFullHistory) lets setPage push the entry — the stamp effect labels it — so
+    // one navigation never costs two Back presses.
+    if (st.sfPage === "channels") {
+      window.history.pushState({ ...st, sfPage: "channels", _chTab: v }, "");
+    }
   }, []);
   const setLayout = useCallback((l: ChannelLayout) => {
     setLayoutState(l);
@@ -154,6 +164,27 @@ export function ChannelsProvider({ children }: { children: ReactNode }) {
     if (page !== "channels") setFocusName(null);
   }, [page]);
 
+  // Label the entry the manager was REACHED on (setPage pushes a bare { sfPage }), so stepping back
+  // onto it later restores the tab it belonged to rather than leaving whatever tab is current.
+  useEffect(() => {
+    if (page !== "channels") return;
+    const st = window.history.state || {};
+    if (st._chTab === undefined) window.history.replaceState({ ...st, _chTab: view }, "");
+  }, [page, view]);
+
+  // Back/Forward across tab entries: restore the tab the entry carries.
+  useEffect(() => {
+    function onPop(e: PopStateEvent) {
+      const tab = e.state?._chTab;
+      if (!tab) return; // an entry outside the manager — leave the tab alone
+      const next = clampView(tab as string);
+      setViewState(next);
+      setAccountRaw(LS.channelsView, next);
+    }
+    window.addEventListener("popstate", onPop);
+    return () => window.removeEventListener("popstate", onPop);
+  }, []);
+
   const state = useMemo<ChannelsState>(
     () => ({ search, statusFilter, view, layout, sort, filtersResetToken, focusName, focusToken }),
     [search, statusFilter, view, layout, sort, filtersResetToken, focusName, focusToken],

frontend/src/components/Pager.tsx

@@ -34,9 +34,17 @@ export default function Pager({
   // Local text for the editable "jump to page" box (committed on Enter/blur).
   const [pageInput, setPageInput] = useState(String(safePage + 1));
   useEffect(() => setPageInput(String(safePage + 1)), [safePage]);
+
+  // Turning the page swaps the whole list, so put the reader at its top — landing mid-list in a page
+  // you haven't seen is disorienting. The page scroller is the app's <main> (the same implicit
+  // contract BackToTop and VirtualGrid's getScrollParent rely on).
+  function goToPage(p: number) {
+    onPageChange(p);
+    document.querySelector("main")?.scrollTo({ top: 0 });
+  }
   function commitPageInput() {
     const n = parseInt(pageInput, 10);
-    if (!isNaN(n)) onPageChange(Math.min(totalPages - 1, Math.max(0, n - 1)));
+    if (!isNaN(n)) goToPage(Math.min(totalPages - 1, Math.max(0, n - 1)));
     else setPageInput(String(safePage + 1));
   }
 
@@ -46,7 +54,7 @@ export default function Pager({
       {totalPages > 1 && (
         <div className="flex items-center gap-2">
           <button
-            onClick={() => onPageChange(Math.max(0, safePage - 1))}
+            onClick={() => goToPage(Math.max(0, safePage - 1))}
             disabled={safePage === 0}
             className="glass-card glass-hover flex items-center gap-1 px-3 py-1.5 rounded-lg disabled:opacity-40 transition"
           >
@@ -69,7 +77,7 @@ export default function Pager({
             {t("datatable.pager.ofTotal", { total: totalPages })}
           </span>
           <button
-            onClick={() => onPageChange(Math.min(totalPages - 1, safePage + 1))}
+            onClick={() => goToPage(Math.min(totalPages - 1, safePage + 1))}
             disabled={safePage >= totalPages - 1}
             className="glass-card glass-hover flex items-center gap-1 px-3 py-1.5 rounded-lg disabled:opacity-40 transition"
           >