fix(frontend): four state defects the deep-review found in the E27 S2 sweep

Every one of them is the same shape: a value derived correctly, and a WRITE to
the thing it derives from left unattended. Deriving hides a stale value; it does
not consume it.

PlayerModal — the watch toggle inherited the previous video's auto-watch. Moving
the queue-advance sync into render was right for `currentVideoId`, but the same
block also synced `status`, and that one had an ordering constraint of its own:
useYtProgress's cleanup for the OUTGOING item can still call setWatched(true)
near the end of a clip, and cleanups run after the commit. As an effect the sync
landed last and corrected it; from render it lands first and the stray write
wins. Press Next in the final ten seconds and the NEXT video showed as watched —
one click on the toggle then sent onState(next, "new") for an item already new.
Fixed by keying the mirror to the id it describes, so a write for another item is
ignored rather than displayed, and no ordering has to be argued about at all.

ChannelsProvider — a focus-channel intent was masked by the page rather than
consumed, and nothing ever cleared it. The manager is a page chunk: it unmounts
on every navigation, and its seed effect runs again on each mount, so returning
to it re-applied a channel name from earlier in the session over whatever the
user had typed since. The consumed marker now lives in the provider, keyed on the
token — which also closes the case the old clear-on-leave effect never handled,
opening a channel page (that does not change `page` at all).

TagFilterChips + ChannelTags x2 — `open = openRaw && hidden > 0` hides the
overflow popover when the lane stops overflowing, but floating-ui only reports a
close for a real event on a mounted surface, so the raw flag stayed true and the
menu came back by itself on the next re-fit — a window resize or the text-size
slider is enough, with nobody near it. The flag is now reset in render against
the same condition that hides it.

Avatar + downloadRow — remembering a failed image BY URL fixed the recycled-row
frame but never forgot it, so a transient 429 pinned a channel to its initial for
the life of the instance, never re-requesting. The memory is now dropped once
`src` moves off it, which keeps both properties.

And playerModalHooks' last exhaustive-deps suppression claimed "nothing in the
body reads a render value" while reading five. The invariant that is actually
load-bearing is that each of them is a per-item snapshot — written down instead.

All four fixes are mutation-checked: each new test was seen red, against the
fixed line only, naming the real defect.

frontend/src/components/PlayerModal.tsx

@@ -234,25 +234,36 @@ export default function PlayerModal({
     setLiveData(null);
   };
 
-  // Local mirror of watch status so the toggle reacts instantly; changes are
-  // propagated to the feed (and server) via onState.
-  const [status, setStatus] = useState(active.status);
-  const watched = status === "watched";
+  // Local mirror of watch status so the toggle reacts instantly; changes are propagated to the feed
+  // (and server) via onState. The mirror carries the id it DESCRIBES, and a write for any other id
+  // is ignored rather than displayed — that is the enforcement, and it has to be in code because
+  // one writer arrives late by construction: useYtProgress's cleanup for the OUTGOING item runs
+  // after the commit that already advanced `active`, and near the end of a clip it auto-marks that
+  // item watched (playerModalHooks.ts `maybeAutoWatch`). Keyed, that stray write is simply not this
+  // item's, so the toggle falls back to `active.status` and no ordering has to be argued about.
+  // Unkeyed it landed last and painted the NEXT video as watched; a corrective click then sent
+  // onState(next, "new") for an item that was already new.
+  const [status, setStatus] = useState<{ id: string; value: VideoStatus }>({
+    id: active.id,
+    value: active.status,
+  });
+  const watched = (status.id === active.id ? status.value : active.status) === "watched";
   const setWatched = (on: boolean) => {
     const next = on ? "watched" : "new";
-    setStatus(next);
+    setStatus({ id: active.id, value: next });
     onState(active.id, next);
   };
 
-  // On queue advance (active changes), sync local state to the new item — DURING that render, not
-  // one commit later. As an effect, the frame between showed the new episode's chrome over the
-  // previous one's watch state and `navigated` flag (currentVideoId still pointed at the old id, so
-  // the "you have navigated away" affordance flashed on every advance). React discards this pass
-  // instead of committing it, so there is no such frame; the guard falsifies itself immediately.
+  // On queue advance (active changes), point `currentVideoId` at the new item — DURING that render,
+  // not one commit later. As an effect, the frame between still had it on the previous id, so the
+  // "you have navigated away" affordance flashed on every advance. React discards this pass instead
+  // of committing it, so there is no such frame; the guard falsifies itself immediately.
+  //
+  // The watch status is NOT synced here: it is keyed by id above, which is both stale-proof and
+  // immune to the late writer this block cannot see (see that comment).
   const [syncedTo, setSyncedTo] = useState(active.id);
   if (syncedTo !== active.id) {
     setSyncedTo(active.id);
-    setStatus(active.status);
     setCurrentVideoId(active.id);
   }