- CreateUser now provisions a default "{name}'s Workspace" for non-invite
signups (email, Google, GitHub, seeder), with the owner as Admin and
current_workspace_id set. Invite signups still skip it (they join the
inviter's workspace on acceptance).
- UserSeeder drops its now-redundant explicit CreateWorkspace call.
- After Stripe checkout, billing/processing lands the user on the social
accounts screen with the connect dialog open (was: calendar), so onboarding
flows straight into connecting an account.
Quantity stays correct (1 workspace → checkout quantity 1). The first workspace
is created without brand details; brand setup remains available in Settings and
on the create-workspace screen for additional workspaces.
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