feat(users): admin can permanently delete users, fix set-password redirect bug

- New DELETE /users/{id}: hard-deletes a user only if they have zero
  activity footprint (no tests, evidence, worklogs, audit entries, Jira
  links, procedure/template suggestions, reviewed imports) — otherwise
  rejects with a clear message to deactivate instead, to keep the audit
  trail intact. Cleans up the user's own notifications/password-setup
  tokens as part of deletion. Self-delete is blocked. Wired to a trash
  icon in the Users page with a confirm dialog.
- Registered the EvaluationImport model in app/models/__init__.py — it
  was missing, so its table never existed in the SQLite test DB; only
  surfaced once the new delete-user footprint check queried it.
- Fixed a redirect bug: the axios response interceptor's on-401 redirect
  to /login didn't exempt /set-password, so the auth provider's routine
  mount-time /auth/me check (401 for a logged-out visitor) bounced anyone
  opening their emailed set-password link away before they could use it.

backend/app/routers/users.py

@@ -36,6 +36,7 @@ from app.services.audit_service import log_action
 # Import  from app.services.user_service
 from app.services.user_service import (
     create_user_without_password,
+    delete_user,
     get_user_or_raise,
     list_users,
     switch_active_role,
@@ -307,6 +308,36 @@ def update_user_route(
     return user
 
 
+# ---------------------------------------------------------------------------
+# DELETE /users/{id}  —  permanently delete a user
+# ---------------------------------------------------------------------------
+
+
+@router.delete("/{user_id}", status_code=status.HTTP_204_NO_CONTENT)
+def delete_user_route(
+    user_id: uuid.UUID,
+    db: Session = Depends(get_db),
+    current_user: User = Depends(require_role("admin")),
+) -> None:
+    """Permanently delete a user. **Requires admin role.**.
+
+    Only users with no activity footprint (no tests, evidence, worklogs,
+    audit entries, etc.) can be hard-deleted — anyone else must be
+    deactivated instead, to preserve the audit trail.
+    """
+    with UnitOfWork(db) as uow:
+        delete_user(db, user_id, current_user.id)
+        log_action(
+            db,
+            user_id=current_user.id,
+            action="delete_user",
+            entity_type="user",
+            entity_id=user_id,
+            details={},
+        )
+        uow.commit()
+
+
 # ---------------------------------------------------------------------------
 # POST /users/{id}/send-password-email  —  set-password / reset link
 # ---------------------------------------------------------------------------