feat: add signup disable config and fix telemetry startup (#3319)

* feat: add signup disable config and fix telemetry startup

* fix: nits for config spread and 403 checks

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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Co-authored-by: Daniel Salazar <daniel.salazar@puter.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/backend/controllers/system/SystemController.test.ts

@@ -233,6 +233,7 @@ describe('SystemController GET /whoarewe', () => {
         expect(captured.body).toMatchObject({
             name: 'Puter',
             environment: 'dev',
+            disable_user_signup: false,
         });
     });
 });