[Organization] Add onboarding process

When the first organizer joins an org, they should be met with an onboarding wizard to fill out their organization profile (and a few important settings; maybe transparency mode).

Then, they get brought to the Organization tour.

Review the first-organizer join flow and the existing Organization tour before defining the onboarding scope. Clarify which organization profile fields and settings belong in the wizard, how transparency mode should work, and what completion should lead to; the issue does not name files or tests.

Written by the indexing model from the issue text.