fix: make auth SQL bootstrap idempotent

[bhudevbhanpuriya]

Summary

This PR makes the auth database bootstrap script idempotent.

In practice, that means database/istsos_auth.sql can be run more than once without failing just because the expected auth objects already exist.

Problem

The script previously assumed it was always running on a fresh database.

Some statements used plain creation commands such as:

ALTER TABLE ... ADD COLUMN ...
CREATE ROLE ...

Those commands succeed the first time, but fail on a later redeploy or retry because PostgreSQL reports that the column, role, or policy already exists.

What Changed

• The initial administrator user insert now uses ON CONFLICT ("username") DO NOTHING.

  • Prevents duplicate admin-user insert failures on rerun.

• Auth-related columns now use ADD COLUMN IF NOT EXISTS.

  • Prevents reruns from failing when user_id or commit_id already exists.

• The user, guest, and sensor database roles are now created only if they do not already exist.

  • Avoids "role already exists" errors.

• Anonymous RLS policies are now checked before creation.

  • Avoids duplicate policy creation errors on rerun.

Expected Result

Running database/istsos_auth.sql multiple times should no longer fail because of already-existing auth bootstrap objects.