Server hardening: nginx origin locked to ArvanCloud + CSP, demo logins removed, docs

- ops/nginx/: the two nginx sites as they now run on 249. Only ArvanCloud
  edges reach the app (direct hits on the IP get 403, so Arvan's DDoS/WAF
  can't be skipped); the frontend gets CSP (own sources only, the one inline
  script by hash), X-Frame-Options, nosniff, Referrer-Policy,
  Permissions-Policy, HSTS; API body limit 100M -> 20M plus HSTS. Checked from
  outside and in Chrome (all tabs and an island quiz, logged in): no CSP errors.
- Demo accounts (users 11-15, 25) and TEST_LOGIN_PHONES removed from the server;
  the health warning for fixed-code logins now has a test and says how to
  test instead (an OTPCode made in the admin).
- SMS daily cap on the server is 2000 (launch of ~600 users).
- CLAUDE.md: never run tests with --parallel on macOS, always --noinput
  (both hang forever without an error).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

config/tests_no_fixed_logins.py

@@ -0,0 +1,20 @@
+"""
+روی سرور هیچ شماره‌ای با کدِ ورودِ ثابت نباید باشد (حساب‌های دمو ۲۰۲۶-۱۰-۱۳ پاک شدند). اگر کسی
+TEST_LOGIN_PHONES را دوباره پر کند، /api/health (با کلید) باید بگوید، نه بی‌صدا بپذیرد.
+"""
+
+from django.test import TestCase, override_settings
+
+
+@override_settings(INTERNAL_SERVICE_KEY='k')
+class FixedCodeLoginsAreFlaggedTests(TestCase):
+    def _warnings(self):
+        return self.client.get('/api/health', HTTP_X_INTERNAL_KEY='k').json()['warnings']
+
+    @override_settings(TEST_LOGIN_PHONES={'09120000001': '834512'})
+    def test_a_fixed_code_phone_raises_a_warning(self):
+        self.assertTrue(any('TEST_LOGIN_PHONES' in w for w in self._warnings()))
+
+    @override_settings(TEST_LOGIN_PHONES={})
+    def test_empty_list_is_quiet(self):
+        self.assertFalse(any('TEST_LOGIN_PHONES' in w for w in self._warnings()))