fix(init): avoid duplicated okdev manifest paths

[acmore]

Summary

• resolve init scaffold output paths through one helper
• keep .okdev/... manifest paths project-root relative when config is .okdev/okdev.yaml
• cover both built-in PyTorchJob scaffolding and template-declared companion files

Tests

• go test ./internal/cli -run 'TestInit.*(FolderConfigAndDotOkdevPath|ScaffoldsPyTorchJobManifest|CustomTemplateRendersDeclaredFile)'
• go test ./internal/config ./internal/cli
• .venv/bin/pre-commit run --all-files --hook-stage manual okdev-gofmt