Add OIDC sign-in, group-derived roles and declarative instance configuration

Workspaces, group mappings and sign-in methods now come from a configuration
file synchronized at startup; workspaces dropped from it are disabled, never
deleted. Instance administrators (a new role) see and help every workspace and
may delete disabled ones; workspace administrators and employees are derived
from the user's groups at every SSO sign-in or administrator edit, and the
employee permission set belongs to the workspace. Self-registration is gone:
users come from SSO (only when their groups map) or from the administrator.
Break-glass bootstrap accounts get an HMAC-derived hourly password that all
replicas agree on. First SSO sign-in links a matching email contact to the
user. The demo runs on the same model with a generated per-start password.

Co-Authored-By: Claude <noreply@anthropic.com>

src/generation_service.rs

@@ -67,6 +67,7 @@ async fn prepare(db: &Store, actor: Uuid, workspace: Uuid, draft: &Draft) -> Res
                 display_name: user.display_name.clone(),
                 email: None,
                 country: Some(user.country.clone()),
+                aliases: vec![],
             });
         }
     }