Record resolved git refs in source info

[yoshifuminakamura]

Summary

• record git source ref metadata as ref_name, ref_kind, and resolved_commit from bk_fetch_source
• use the resolved ref metadata for build cache source validation
• update result JSON handling, Portal source displays, tests, and docs to describe branch/tag refs

Notes

• App build scripts continue to call bk_fetch_source the same way; the third argument may be a branch or tag.
• Existing build cache entries without the new ref metadata will miss once and be rebuilt.

Validation

• bash -n scripts/bk_functions.sh scripts/build_with_cache.sh scripts/result.sh scripts/tests/test_bk_fetch_source.sh
• shellcheck -S error scripts/bk_functions.sh scripts/build_with_cache.sh scripts/result.sh scripts/tests/test_bk_fetch_source.sh
• bash scripts/tests/test_bk_fetch_source.sh
• bash scripts/tests/test_build_cache.sh
• .venv/bin/python result_server/tests/run_result_server_tests.py
• profile-data-shell test suite equivalent
• python3 scripts/tests/check_text_integrity.py
• python3 scripts/tests/check_commit_messages.py
• git diff --check