fix(pr-review): preserve addressed findings

[Troublor]

Summary

• track code-level finding status separately from GitHub thread resolution status
• preserve addressed findings when thread resolution was intentionally skipped, while still detecting manually reopened confirmed threads
• keep omitted prior findings conservatively open and reject unknown or duplicate finding IDs
• load Claude actions from the trusted main branch instead of the PR checkout

Test plan

• PYTHONDONTWRITEBYTECODE=1 python3 -m unittest discover -s .github/actions/claude-pr-review -p 'test_*.py' -v
• actionlint -shellcheck='' .github/workflows/claude.yml .github/workflows/build-check.yml
• git diff --check

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This PR was generated by an automated agent.