* feat(auth): proxy OIDC provider icons server-side (#1333)
Strict img-src CSP blocked external OIDC icon hosts on the login page.
Loosening CSP was rejected via the MakerWorld precedent, so icons are
proxied: admin sets icon_url, backend fetches and caches the bytes in a
deferred BLOB column, the SPA renders from a same-origin
/api/v1/auth/oidc/providers/{id}/icon endpoint.
fix(oidc): use preferred_username/name claim for auto-created username
When auto-creating an OIDC user without a valid email claim, derive the
username from preferred_username or name IdP claims instead of falling
back to the opaque provider_sub[:30].
feat(oidc): add Azure Entra ID support with configurable email claim resolution
Adds two new OIDC provider fields: email_claim and require_email_verified.
Sn0rrii