Add a new `session_id` output that exposes the Claude Code session ID,
allowing other workflows or Claude Code instances to resume the
conversation using `--resume <session_id>`.
Changes:
- Add parseAndSetSessionId() function to extract session_id from
the system.init message in execution output
- Add session_id output to both action.yml and base-action/action.yml
- Add comprehensive tests for the new functionality
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Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>