Audit 2026-06-02: `_load_or_create_key` silently minted a new Fernet
key whenever the key file was missing — no log, no warning. The
failure mode the audit flagged: a partial disaster restore where the
DB was restored but `/images/secrets/` was lost would produce a
working-looking system in which every authenticated download fails
AUTH_ERROR until the operator re-uploads every credential by hand.
Two opt-ins now needed for auto-creation:
1. Explicit `bootstrap_ok=True` kwarg (tests, scripts), OR
2. `CURATOR_BOOTSTRAP_NEW_KEY=1` env var (operator first-time setup)
Otherwise the constructor raises `MissingCredentialKey` so the app
fails fast at startup and the operator can restore the key file
from backup before encrypted_blob rows go undecryptable.
Also: docstring path was wrong (said "images/data root" but actual
location is `/images/secrets/credential_key.b64`) — corrected.
Tests updated to pass `bootstrap_ok=True` explicitly, and two new
tests cover the safety behavior (missing-key-raises, env-var-bootstraps).
bvandeusen