fix: add header length constraint to question.txt

[pschiel]

Fixes #7616

Cause: agents sometimes violate the 12-character header limit because JSON Schema constraints like "maxLength": 12 are buried in nested parameter definitions and have lower attention weight compared to prominent natural language instructions in the tool description, causing the LLM occasionally to miss or forget the constraint during generation.

Fix: add it to description text in question.txt

[github-actions[bot]]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found