chore: update OpenAPI spec from monorepo (#479)

Co-authored-by: OpenRouter SDK Bot <sdk-bot@openrouter.ai>

Author: openrouter-docs-sync[bot]

.speakeasy/in.openapi.yaml

@@ -23115,6 +23115,8 @@ components:
         model:
           type: 'string'
         prompt:
+          description: 'Text prompt describing the video to generate. Optional for models that support generating a video from image input alone; required by all other models.'
+          example: 'A serene mountain landscape at sunset'
           type: 'string'
         provider:
           description: 'Provider-specific passthrough configuration'
@@ -23146,7 +23148,6 @@ components:
           example: '1280x720'
           type: 'string'
       required:
-        - 'prompt'
         - 'model'
       type: 'object'
     VideoGenerationResponse: