[vishr]

What changed

Reverts #432. FANOUT_FIRST_ADMIN_EMAIL has not been in any release, so nobody depends on it.

Automated installs will create accounts through SCIM provisioning (#442), which links the identity directly. That avoids matching an account by email address and the window where whoever controls the mailbox claims the administrator account.

First boot returns to the setup URL. .env.example and the settings reference are regenerated.

Refs #427

Verification

• go test for internal/auth, internal/config, internal/api, internal/settings, internal/ingest, and cmd/fanout passes.
• The pre-push just check passes.
• No reference to the setting remains in the repository.
• The diff against the commit before feat(auth): designate the first administrator with FANOUT_FIRST_ADMIN_EMAIL #432 matches the changes merged since feat(auth): designate the first administrator with FANOUT_FIRST_ADMIN_EMAIL #432, line for line, in every file feat(auth): designate the first administrator with FANOUT_FIRST_ADMIN_EMAIL #432 touched. Nothing else moved.