Local auth stays the primary/always-available login (don't want to
lock out the saved admin password) — OIDC is additive, shown as a
second button when OIDC_ENABLED=true. Uses openid-client v6 with PKCE.
Authentik-side provider was set up via an authentik blueprint (its own
declarative automation, see docs/oidc-setup.md) rather than touching
any existing admin credentials.
Closes#12.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
