codex: scope implicit resume-last selection to the current Claude session

[VOIDXAI]

Closes #81

Summary

• scope implicit --resume-last selection to the current Claude session when a Claude session id is present
• reuse the same session-aware selection logic for task-resume-candidate and task --resume-last
• stop tasks from other sessions from being resumed implicitly or blocking the current session

Testing

• node --test --test-name-pattern 'task-resume-candidate|task --resume-last|task --resume acts like --resume-last' tests/runtime.test.mjs
• npm test