docs: Mintlify MDX docs + docs.json; bump Speakeasy to 1.787.0 (#382)

docs/operations/arena.mdx

@@ -0,0 +1,23 @@
+---
+title: "Arena"
+---
+
+Design Arena only: arena to query. Defaults to `models` when source is `design-arena`.
+
+## Example Usage
+
+```python
+from openrouter.operations import Arena
+
+# Open enum: unrecognized values are captured as UnrecognizedStr
+value: Arena = "models"
+```
+
+
+## Values
+
+This is an open enum. Unrecognized values will not fail type checks.
+
+- `"models"`
+- `"builders"`
+- `"agents"`