Extend 04-shared-identity's UI test to not just assert team@example.org is
offered but to actually select it as the sender and confirm it becomes the
active From identity, then hold on the composer so the selected group address is
visible in the recorded video. Adds selectComposerFrom / selectedComposerFrom
helpers.
Provision a Stalwart group (team@example.org) with carol as a member before her
first login, and assert the composer's From selector offers the group address.
This confirms the group-membership scenario of #569 already works out of the
box: Stalwart returns the group's send-as identity on the member's own account,
so the app's normal single-account identity load surfaces it (identities.length
> 1 -> the From <select> renders with team@).
- stalwart: create the `team` Group in plan-accounts and add carol via
User.memberGroupIds in the entrypoint (id resolved after apply, like
DOMAIN_ID). carol, not alice/bob, so the sync specs stay unshared.
- helpers: GROUP config, openComposer/composerFromOptions, and JmapClient
accounts + sharedAccountNames (Identity/get needs the submission capability).
- composer: add data-testid="composer-from" to the From <select> and its
single-identity <span> fallback.
Ref: https://github.com/bulwarkmail/webmail/issues/569
