Use the parent issue as the casting brief for /squad cast #1634

Summary

When a user writes a detailed issue describing the Squad they want, then comments /squad cast, Cast mode should treat the parent issue title and body as the explicit casting brief.

Current behavior

For an issue_comment trigger, the workflow reads /squad cast from the comment and primarily derives the team from repository analysis. The prompt does not explicitly require reading or honoring the parent issue description, so a carefully articulated team request may be ignored.

Desired behavior

• For an issue comment, read the parent issue title and body as the casting brief.
• For a command in an issue body, treat the content following /squad cast as the brief.
• Treat explicit requested roles, responsibilities, constraints, team size, and operating model as requirements.
• Use repository analysis to refine and validate the brief, not silently override it.
• Resolve conflicts explicitly or explain necessary adaptations.
• In the generated PR, summarize how each requested role or capability was represented.
• Preserve the existing repository-driven Cast behavior when no meaningful brief is provided.

Example

1. A user opens an issue containing a detailed team structure for a specialized planning or review Squad.
2. The user comments /squad cast.
3. The generated Squad reflects that issue's requested structure, augmented with relevant repository context.

This would make issues reusable, reviewable specifications for point-in-time Squad composition.