Add a fallback when fork tokens cannot post comments

[Pybsama]

Summary

• catch the known Resource not accessible by integration error when a fork workflow token cannot create or update a comment
• emit a GitHub warning and log the complete comment that would have been posted
• add the same message to the Actions Job Summary when it is available
• preserve the original exit code and stderr for every other command failure
• route all seven PR, Issue, and Discussion create/update paths through the fallback
• make top-level Discussion comments use the helper's explicit ID and message arguments

Fixes #44.

Testing

• added Bash subprocess tests for success, the known fork permission error, unexpected failures, multiline argument preservation, and top-level Discussion parameters
• confirmed the fallback tests fail against the previous implementation before the helper exists
• npm ci && npm test — 10 tests passed
• focused test file repeated 20 times
• bash -n queries.sh
• parsed action.yml with js-yaml
• git diff --check