docs: add final demo admin seed and release notes for submission read…

[AlperKartkaya]

Summary

This PR prepares the repo-side final submission requirements by ensuring the normal migration flow includes a working demo admin account and by
documenting final release credentials and notes.

Resolves #624

Changes

• Added a normal backend migration that seeds:
  • bogazici_admin@neph.test
  • password: DemoPass123!
  • role: SUPER_ADMIN
• Updated README.md with final demo credentials for admin, requester, and volunteer users.
• Added docs/releases/final-milestone-release-notes.md as a ready-to-copy GitHub Release description for 1.0.0.

Validation

• Ran migrations against an isolated temporary Postgres database.
• Verified the admin row is created with SUPER_ADMIN.
• Verified real login through POST /api/auth/login returns 200 and an access token for bogazici_admin@neph.test.
• Ran docker compose config --quiet.
• Ran git diff --check.

Notes

External release steps are still required separately: merge to main, create/push final-milestone, create the official 1.0.0 GitHub Release, and
attach the signed Android APK.

[mehmetcangurbuz08]

Looks necessary. Merging.