feat: add support for openai/gpt-5-pro model

Adds configuration for the new GPT-5 Pro model released by OpenAI.

Specifications from official docs:
- 400K context window
- 272K max output tokens (largest of GPT-5 family)
- Highest reasoning capability (5/5)
- Reasoning token support
- Vision input support (text+image input, text output only)
- No temperature support (fixed, like other reasoning models)
- Available via Responses API only (use_openai_response_api: true)
- Default reasoning effort: high

Accessible via alias 'gpt5pro'.

conf/openrouter_models.json

@@ -16,6 +16,8 @@
       "max_image_size_mb": "Maximum total size in MB for all images combined (capped at 40MB max for custom models)",
       "supports_temperature": "Whether the model accepts temperature parameter in API calls (set to false for O3/O4 reasoning models)",
       "temperature_constraint": "Type of temperature constraint: 'fixed' (fixed value), 'range' (continuous range), 'discrete' (specific values), or omit for default range",
+      "use_openai_response_api": "Set to true when the model must use the /responses endpoint (reasoning models like GPT-5 Pro). Leave false/omit for standard chat completions.",
+      "default_reasoning_effort": "Default reasoning effort level for models that support it (e.g., 'low', 'medium', 'high'). Omit if not applicable.",
       "description": "Human-readable description of the model",
       "intelligence_score": "1-20 human rating used as the primary signal for auto-mode model ordering"
     }
@@ -292,6 +294,25 @@
       "description": "GPT-5 (400K context, 128K output) - Advanced model with reasoning support",
       "intelligence_score": 16
     },
+    {
+      "model_name": "openai/gpt-5-pro",
+      "aliases": [
+        "gpt5pro"
+      ],
+      "context_window": 400000,
+      "max_output_tokens": 272000,
+      "supports_extended_thinking": true,
+      "supports_json_mode": true,
+      "supports_function_calling": true,
+      "supports_images": true,
+      "max_image_size_mb": 20.0,
+      "supports_temperature": false,
+      "temperature_constraint": "fixed",
+      "use_openai_response_api": true,
+      "default_reasoning_effort": "high",
+      "description": "GPT-5 Pro - Advanced reasoning model with highest quality responses (text+image input, text output only)",
+      "intelligence_score": 17
+    },
     {
       "model_name": "openai/gpt-5-codex",
       "aliases": [