fix(desktop): refresh channel state after unarchive

[wesbillman]

Problem

Unarchiving a channel succeeds on the relay, but the desktop UI keeps showing the channel as archived in the channel browser/search and leaves the message composer disabled. Verified the relay side is correct: the unarchived channel reports archived_at: null, and both the send-gate and channel-list/search read archived_at fresh from the DB.

Root cause

In desktop/src/features/channels/hooks.ts there's an asymmetry between the archive and unarchive mutations:

• useArchiveChannelMutation patches the cache optimistically (onSuccess) and invalidates/refetches via onSettled → invalidateChannelState.
• useUnarchiveChannelMutation only did the optimistic patch — no onSettled.

The optimistic patch updates channelsQueryKey and the detail query in place, but doesn't reconcile against the relay. The channel browser reads the list query and the composer gate reads the detail query; with useChannelsQuery on a 60s staleTime/refetchInterval, the stale archived state sticks until an unrelated refetch fires.

Fix

Give the unarchive mutation the same onSettled: invalidateChannelState the archive mutation already has, so the channel list, detail, and members queries refetch from the relay after a successful unarchive.

       setChannelArchivedState(queryClient, channelId, null);
     },
+    onSettled: async () => {
+      await invalidateChannelState(queryClient, channelId);
+    },
   });
 }

Verification

• tsc --noEmit — clean
• biome lint (changed file) — clean
• pnpm test — 585/585 pass
• pre-push hook suite (rust-tests, clippy, desktop/mobile/tauri tests) — all green

Note on tests

No regression test added. The desktop suite runs node's built-in test runner over *.test.mjs for pure-logic modules — there's no React/renderHook/QueryClient harness, so testing this React Query lifecycle wiring would require standing up a new harness, disproportionate to a one-line symmetry fix. Happy to add the harness + a mutation-lifecycle test as a follow-up if desired.