After read access is granted the wizard now imports the user's YouTube
subscriptions automatically (with a "Building your feed…" progress state), so a
new user lands on a populated feed — channels already in the shared catalog show
up instantly, new ones backfill in the background. The empty feed now prompts
users without read access to set up via the wizard instead of a bare message.
After the clean name/email sign-in, a wizard walks the user through granting
YouTube read (then optionally write) one step at a time, each with a plain
rationale and an up-front heads-up about Google's "unverified app" screen.
The visible step is derived from the granted scopes (can_read/can_write) so the
flow resumes correctly across the full-page consent redirect; it's dismissible
and reopenable from Settings -> Account, which now lists read and write as
separate, individually-grantable access rows.
