feat: Phase 4 models + files — CRUD, multipart upload, signed URLs
Add model and file management:
- model/model.go: ModelCard (unified base/fine-tuned), ModelCapabilities
- file/file.go: File, ListParams, Purpose/SampleType/Source enums
- ListModels, GetModel, DeleteModel service methods
- UploadFile (multipart/form-data), ListFiles (query params), GetFile,
DeleteFile, GetFileContent (binary stream), GetFileURL (signed URL)
- doMultipart() HTTP helper for file uploads
- 13 new tests covering all endpoints including multipart parsing
vikingowl
75a726cbe2