Update stale API endpoints and model chains

- Instagram: migrate /v1/ to /v2/ ScrapeCreators endpoint (v1 deprecated Feb 2026)
- OpenAI: switch fallback chain to [gpt-5-mini, gpt-4.1-mini, gpt-4.1] (8x cheaper,
  gpt-5-mini is the first mini model supporting web_search with filters.allowed_domains)
- xAI: use explicit grok-4-1-fast-non-reasoning (bare name aliases to reasoning variant)
- xAI: pass from_date/to_date natively to x_search tool config instead of prompt-only
- Polymarket: correct rate limit comment (15K/10s, not 350/10s)

tests/test_openai_reddit.py

@@ -64,13 +64,13 @@ class TestIsModelAccessError(unittest.TestCase):
 class TestModelFallbackOrder(unittest.TestCase):
     """Tests for MODEL_FALLBACK_ORDER constant."""
 
-    def test_contains_gpt4o(self):
-        """Fallback list should include gpt-4o."""
-        self.assertIn("gpt-4o", MODEL_FALLBACK_ORDER)
+    def test_contains_gpt41(self):
+        """Fallback list should include gpt-4.1 as last resort."""
+        self.assertIn("gpt-4.1", MODEL_FALLBACK_ORDER)
 
-    def test_gpt41_is_first(self):
-        """gpt-4.1 should be the first fallback option."""
-        self.assertEqual(MODEL_FALLBACK_ORDER[0], "gpt-4.1")
+    def test_gpt5_mini_is_first(self):
+        """gpt-5-mini should be the first fallback option (cheapest with web_search support)."""
+        self.assertEqual(MODEL_FALLBACK_ORDER[0], "gpt-5-mini")
 
 
 if __name__ == "__main__":