fix: remove dead imports shadowed by local redefinitions in build_stream

[harshadkhetpal]

Summary

Several names in build_stream/ are imported and then immediately shadowed by local redefinitions (ruff F811), leaving dead imports that contradict the code's own intent:

1. api/{build_image,local_repo,validate}/dependencies.py — each imports _get_container and then redefines it locally with a comment saying the local version exists to avoid circular imports. The import in the list re-creates exactly the coupling the comment says it avoids, and the local def wins anyway. Removed _get_container from the three import lists.
2. container.py — imports _DEFAULT_POLICY_PATH, _DEFAULT_SCHEMA_PATH from core.catalog.adapter_policy, then redefines both from the local resources directory ~40 lines later. The redefinitions win; removed the dead import.
3. orchestrator/local_repo/use_cases/create_local_repo.py — two method-local from core.jobs.value_objects import StageState re-imports that shadow the module-level import of the same name; removed.

Testing

python -m py_compile passes on all five files; ruff check --select F811 on build_stream/ (excluding tests) goes clean. No runtime behavior change — every removed name was shadowed before use.

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