fix(models): rebase relocated submodel paths

[wunianze666-netizen]

Summary

• Fix remote SDNQ pipeline installs retaining absolute submodel paths from the tmpinstall_* staging directory after the pipeline is moved into the managed models directory.
• Rebase a recorded component onto the loader's resolved current model root only when the recorded path is missing and the same-named component exists under that root.
• Preserve valid external component paths, arbitrary model_index.json component names, and the existing failure behavior when neither path exists.

The installer probes the downloaded pipeline before install_path() moves it. Identification records absolute paths for direct child components, while registration updates only the top-level model path and stores managed paths relative to the models directory. Later, the shared resolver therefore returns a deleted staging path, which Transformers interprets as a Hub repository identifier. The resolved loader fallback—not the persisted relative config.path—is the authoritative current root.

Related Issues / Discussions

Closes #9580

QA Instructions

The relocation regression fails before the final implementation when it models a managed record with relative config.path: the resolver returns the deleted staging path instead of the installed component. It passes after the resolver derives the absolute root from fallback.parent.

After the fix:

python -m pytest tests/backend/model_manager/load/test_load_default_helpers.py tests/backend/model_manager/configs/test_z_image_sdnq_identification.py tests/backend/model_manager/configs/test_sdnq_pipeline_submodel_discovery.py -o addopts= -p no:cov -q
63 passed

python -m ruff check invokeai/backend/model_manager/load/load_default.py tests/backend/model_manager/load/test_load_default_helpers.py
All checks passed!

python -m ruff format --check invokeai/backend/model_manager/load/load_default.py tests/backend/model_manager/load/test_load_default_helpers.py
2 files already formatted

git diff --check and the focused sensitive-path scan also pass. The pytest run emits one existing pytest-asyncio configuration warning unrelated to this change.

Merge Plan

No special merge plan is required; this is a focused loader-path fix with regression coverage.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• Changes to a redux slice have a corresponding migration (not applicable)
• Documentation added / updated (if applicable) (not applicable; behavior is covered by tests)
• Updated What's New copy (if doing a release after this PR) (not applicable)

AI-assisted tooling was used to trace the install lifecycle and develop the focused patch and tests; all listed checks were run against the submitted commit.