feat(header): move the sync status into a chip on the header

The rail spent a two-row block plus a divider on per-user sync status. It's
global, not per-module, so it now rides the right end of the floating header as
a pill: the headline count at a glance, an accent dot when something wants you
(paused / missing history), and the counts, state, the channel-manager link and
pause in a popover.

Frees the rail's whole top block. Also drops SyncStatus's two now-dead layouts:
"bar" was a leftover of the top bar removed in 0.42.0, and "rail" lost its only
caller here — the component is chip-only, ~60 lines lighter, and the popover
reuses useDismiss.

frontend/src/components/NavSidebar.tsx

@@ -34,7 +34,6 @@ import { useHoverFocusWithin } from "../lib/useHoverFocusWithin";
 import { type LangCode } from "../i18n";
 import AvatarImg from "./Avatar";
 import LanguageSwitcher from "./LanguageSwitcher";
-import SyncStatus from "./SyncStatus";
 
 // Primary app navigation: a collapsible left rail with icon+label entries (Design C). The
 // modules used to hide under the avatar dropdown; they now live here. Collapsed, it becomes
@@ -48,7 +47,6 @@ export default function NavSidebar({
   language,
   collapsed,
   onToggleCollapse,
-  onGoToFullHistory,
 }: {
   me: Me;
   page: Page;
@@ -60,7 +58,6 @@ export default function NavSidebar({
   // it and asks App to flip it.
   collapsed: boolean;
   onToggleCollapse: () => void;
-  onGoToFullHistory: () => void;
 }) {
   const { t } = useTranslation();
   // When unpinned, the rail sits slim (icons only) and peeks open into a labelled overlay on hover
@@ -306,16 +303,6 @@ export default function NavSidebar({
         </button>
       </div>
 
-      {/* Per-user sync status (video counts + live sync state), moved out of the old top bar. */}
-      <div className="mb-3 pb-3 border-b border-border">
-        <SyncStatus
-          isAdmin={me.role === "admin"}
-          onGoToFullHistory={onGoToFullHistory}
-          variant="rail"
-          collapsed={slim}
-        />
-      </div>
-
       <div
         ref={listFade.ref}
         className="flex-1 min-h-0 overflow-y-auto no-scrollbar flex flex-col gap-1"