Prefix fire-and-forget calls (PubSub.broadcast, Oban enqueue, Logger,
update_*, etc.) with `_ =` so dialyzer knows the return value is
intentionally discarded. Wrap a few if/case expressions whose
branches produce mixed types the same way.
No behavior changes — only explicit acknowledgement of discarded
returns.
Warnings: 242 → 88.
- Remove auto-confirmation on registration (register_user and register_user_with_organization)
- Add deliver_user_confirmation_instructions/2 and confirm_user/1 to Accounts context
- Add verify_email_token_query/2 and by_user_and_contexts_query/2 to UserToken
- Make deliver_confirmation_email public in UserNotifier
- Send confirmation email after registration in both flows
- Block unconfirmed users at password login with helpful message
- Add UserConfirmationController with confirm/resend routes
- Add resend confirmation link to login page
- Update test fixtures to confirm users after registration
