fix(nav): a navigation closes every overlay before it pushes

The overlay history stack let a navigation land ABOVE open overlays and
"buried" their entries with a counter. Measured in Chrome: Shift+W over
About navigated under the still-open dialog, the next Back both undid the
navigation and closed About, and the Back after that did nothing; Shift+W
on Home with the player open did nothing at all. The counter could also be
spent by a different overlay closing first, and callers that could not
report whether they pushed were assumed to have.

setPage and openChannel now close every open overlay and push only once
the history is back in sync (one entry per live overlay, no programmatic
back() in flight, no reconcile queued), so nothing is ever buried and the
whole mechanism goes: navigateOverOverlays, closeThenNavigate, buryUnder,
setPage's boolean, and the three test files that pinned them. The palette
closes only itself before running a row, so a theme picked over the player
keeps the player. Shift+W on Home with the player open now closes it
(owner decision 2026-09-09).

The wait is on state, not on "a popstate": the old 250 ms fallback could
run with back()s still in flight. An overlay that refuses to close within
1.5 s drops the command instead of being navigated out from under.

frontend/src/components/ChannelNameLink.tsx

@@ -11,7 +11,7 @@ import { urlWithParams } from "../lib/urlState";
 // The href is the same URL `openChannel` pushes — `?chan=<id>` on the current page — so a new tab
 // lands where the in-app navigation would have. A plain left click is still handled in-app, because
 // the SPA path does more than navigate (the player has to close first and reclaim its own
-// Back-to-close history entry; see closeThenNavigate).
+// Back-to-close history entry; see lib/history.closeOverlaysThenNavigate).
 type Props = Omit<AnchorHTMLAttributes<HTMLAnchorElement>, "href" | "onClick" | "title"> & {
   channelId: string;
   title: string | null | undefined;