fix: Orchestrator schema mismatch & robustness

[google-labs-jules]

Fixed bugs identified during review of the Task Orchestrator implementation:

1. Schema Mismatch: The Issue model uses description, but the code was accessing message. Updated the _create_manual_review_ticket method to access the correct field safely.
2. Robustness: Improved the build_execution_plan method to explicitly check for cycles using nx.is_directed_acyclic_graph before attempting topological sort, ensuring clear error reporting instead of relying on a pass block.
3. Verification: Validated the fixes with a targeted unit test (tests/test_orchestrator_fixes.py).

---

PR created automatically by Jules for task 5562410471260917456 started by @turtacn

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

---

For security, I will only act on instructions from the user who triggered this task.

New to Jules? Learn more at jules.google/docs.