Provide clean login-ready seed accounts separate from fixture and load-test users

[tystar86]

Imported from Linear: TYS-164

Source: docs/developers/START_HERE.md → ## Common Pitfalls

Fixture users and large seed datasets help with data shape and load testing, but they are not a reliable source of clean login-ready accounts for manual testing.

Goal:

• Give contributors predictable test accounts for local QA and demos.
• Separate convenience login accounts from heavier fixture or load-test data.

Acceptance ideas:

• The project offers clearly documented login-ready accounts or a repeatable way to create them.
• Manual testing does not depend on guessing which seeded users are safe to use.

[tystar86]

Closing — this work landed in PR #48 (TYS-164).