make db rotates the Postgres password on every run

`bin/setup_litellm_db.py:133` generates a fresh password on every invocation
and `ALTER ROLE`s it, then prints the `database_url` for manual pasting into
`litellm.yaml`.

So running `make db` twice — or after any unrelated config edit — silently
breaks a working `litellm.yaml`. The failure surfaces as:

```
Authentication failed against database server at `127.0.0.1`,
the provided database credentials for `llmao` are not valid.
```

which points at credentials rather than at the script that changed them. The
proxy gets far enough to register both models from YAML before dying, so the
config looks fine.

**Fix:** read the existing password out of `litellm.yaml` when one is present
and reuse it, generating only when the role does not exist. Or write the value
back into `litellm.yaml` rather than printing it.

**Workaround:** re-run `make db` and paste the new `database_url`, or set the
role to match the file already in place:

```bash
sudo -u postgres psql -c "ALTER ROLE llmao PASSWORD ''"
```

Not an issue under Puppet — the manifest generates the password from eyaml and
creates the role with it, so the two cannot drift.

Start with bin/setup_litellm_db.py:133 and inspect how it generates and applies the password, then check the existing database_url in litellm.yaml. Run make db twice with an existing role and configuration; done means the second run does not invalidate the credentials used by litellm.yaml and the proxy can authenticate.

Written by the indexing model from the issue text.