Fix o3-pro model resolution to use o3-pro consistently

- Use o3-pro throughout the codebase instead of o3-pro-2025-06-10
- Update test expectations to match o3-pro model name
- Update cassette to use o3-pro for consistency
- Ensure responses endpoint routing works correctly with o3-pro

🤖 Generated with [Claude Code](https://claude.ai/code)

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

tests/openai_cassettes/o3_pro_basic_math.json

@@ -23,7 +23,7 @@
               "role": "user"
             }
           ],
-          "model": "o3-pro-2025-06-10",
+          "model": "o3-pro",
           "reasoning": {
             "effort": "medium"
           },