Issue remediation: runtime lifecycle

[codejasleen]

This issue tracks the runtime lifecycle implementation for the Issue Remediation design discussed in #6522

Goal

Implement the runtime behavior for Issue remediation.

Scope

• Wire issue remediation into the action factory.
• Create issues.
• Assign issues.
• Persist remediation metadata.
• Close resolved issues.
• Reopen manually closed issues.
• Template interpolation.
• Tests.

Future considerations

The implementation should remain extensible for future enhancements such as labels, comments, and accepted-risk ("Won't Fix") workflows.

Proposed implementation plan

To keep review size manageable, I currently expect this issue to be implemented across multiple PRs:

1. Runtime skeleton and action factory wiring.
2. Issue creation and metadata persistence.
3. Issue lifecycle transitions (reopen/close).
4. Assignment workflow, template interpolation, and follow-up tests.

The exact split may be adjusted based on feedback.