feat(models): add Claude Fable 5 to registry

- Added new model `Claude Fable 5` to `models.json` with enhanced reasoning and long-horizon capabilities.
- Included detailed parameters such as context length, max completion tokens, and thinking level configurations.

Author: luispater

internal/registry/models/models.json

@@ -118,6 +118,29 @@
         ]
       }
     },
+    {
+      "id": "claude-fable-5",
+      "object": "model",
+      "created": 1781049600,
+      "owned_by": "anthropic",
+      "type": "claude",
+      "display_name": "Claude Fable 5",
+      "description": "Anthropic's most capable widely released model, for the most demanding reasoning and long-horizon agentic work",
+      "context_length": 1000000,
+      "max_completion_tokens": 128000,
+      "thinking": {
+        "min": 1024,
+        "max": 128000,
+        "zero_allowed": true,
+        "levels": [
+          "low",
+          "medium",
+          "high",
+          "xhigh",
+          "max"
+        ]
+      }
+    },
     {
       "id": "claude-opus-4-5-20251101",
       "object": "model",