chore: update test fixtures and frontend for UUID identity (refs #217)

Backend test fixtures:
- Replace auth0|xxx format with UUID in all test userId values
- Update admin tests for new id/userProfileId schema
- Add missing deletionRequestedAt/deletionScheduledFor to auth test mocks
- Fix admin integration test supertest usage (app.server)

Frontend:
- AdminUser type: auth0Sub -> id + userProfileId
- admin.api.ts: all user management methods use userId (UUID) params
- useUsers/useAdmins hooks: auth0Sub -> userId/id in mutations
- AdminUsersPage + AdminUsersMobileScreen: user.auth0Sub -> user.id
- Remove encodeURIComponent (UUIDs don't need encoding)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/features/auth/tests/integration/auth.integration.test.ts

@@ -19,6 +19,7 @@ jest.mock('../../../../core/plugins/auth.plugin', () => {
   return {
     default: fastifyPlugin(async function (fastify) {
       fastify.decorate('authenticate', async function (request, _reply) {
+        // JWT sub is still auth0|xxx format
         request.user = { sub: 'auth0|test-user-123' };
       });
     }, { name: 'auth-plugin' }),