create: Clean up experimental paths, fix create from existing safetensor model (#14679)

* create:  Clean up experimental paths

This cleans up the experimental features, and adds both unit and integration test coverage to verify no regressions.

* create: preserve config and layer names when creating from safetensors models

When creating a model FROM an existing safetensors model, ModelFormat,
Capabilities, and layer Name fields were lost. ModelFormat stayed empty
because it's only set from GGML layers (which safetensors models lack),
and layer names weren't copied in parseFromModel. This caused derived
models to fail loading ("config.json not found in manifest").

* review comments

.gitignore

@@ -15,3 +15,4 @@ __debug_bin*
 llama/build
 llama/vendor
 /ollama
+integration/testdata/models/