Add environment snapshot indexing

[yoshifuminakamura]

Summary

Adds the first environment snapshot path for Portal-triggered and generated CI results.

Changes

• Collect lightweight environment snapshots from generated GitLab CI build/run/build_run wrappers
• Keep application build.sh and run.sh scripts untouched
• Combine snapshot artifacts into a Result JSON environment_snapshot reference block
• Index snapshots by canonical SHA-256 hash in the Portal SQLite DB
• Link received results to snapshots through environment_snapshot_results
• Show snapshot summary fields on result detail pages
• Update handoff docs to describe environment snapshots as result-time evidence, not profile policy

Validation

• .venv/bin/python result_server/tests/run_result_server_tests.py
• .venv/bin/python result_server/tests/check_site_config.py
• shellcheck -S error scripts/collect_environment_snapshot.sh scripts/result.sh scripts/matrix_generate.sh scripts/result_server/process_and_send_results.sh scripts/tests/test_process_and_send_results.sh
• bash scripts/tests/test_process_and_send_results.sh