Add PDF support to OpenRouter provider for Opus 4.7

Adds KilnMimeType.PDF to multimodal_mime_types and sets
multimodal_requires_pdf_as_image=True (OpenRouter's PDF routing through
Mistral OCR breaks LiteLLM parsing, so PDFs must be sent as images).

https://claude.ai/code/session_01Xnfzt91McoMdqaiRv1g6xg

Author: claude

libs/core/kiln_ai/adapters/ml_model_list.py

@@ -1936,7 +1936,9 @@ class KilnModel(BaseModel):
                 supports_doc_extraction=True,
                 supports_vision=True,
                 multimodal_capable=True,
+                multimodal_requires_pdf_as_image=True,
                 multimodal_mime_types=[
+                    KilnMimeType.PDF,
                     KilnMimeType.TXT,
                     KilnMimeType.MD,
                     KilnMimeType.JPG,