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/models/__init__.py

@@ -49,6 +49,7 @@ from app.models.procedure_suggestion import ProcedureSuggestion
 from app.models.template_suggestion import TemplateSuggestion
 from app.models.user import User
 from app.models.password_setup_token import PasswordSetupToken
+from app.models.evaluation_import import EvaluationImport
 
 # Assign __all__ = [
 __all__ = [
@@ -94,4 +95,5 @@ __all__ = [
     "ProcedureSuggestion",
     "TemplateSuggestion",
     "PasswordSetupToken",
+    "EvaluationImport",
 ]