BUG (FB3): the channel page's Subscribe mutation had no onError, so a read-only
user (no YouTube write scope) clicking Subscribe got a silent 403 — nothing
happened, no toast. Wire notifyYouTubeActionError (no wizard handle here, so the
message without the Connect button). Block is a local-only action and can't 403
for scope, so it's left as-is.
BUG (FB4): subscribe.onSuccess invalidated channel/feed/channels but omitted
my-status and discovered-channels (which ChannelDiscovery invalidates for the
same action), so after subscribing from a channel page the Discovery list and
the manager stats stayed stale. Added both.
tsc green, localdev boots healthy.
970e725d39