feat: Implement stale validation cleanup and improve GitHub issue handling

- Added a scheduled task to clean up stale validation entries every hour, preventing memory leaks.
- Enhanced the `getAllValidations` function to read validation files in parallel for improved performance.
- Updated the `fetchLinkedPRs` function to use `spawn` for safer execution of GitHub CLI commands, mitigating shell injection risks.
- Modified event handling in the GitHub issues view to utilize the model for validation, ensuring consistency and reducing stale closure issues.
- Introduced a new property in the issue validation event to track the model used for validation.

libs/types/src/issue-validation.ts

@@ -101,6 +101,8 @@ export type IssueValidationEvent =
       issueTitle: string;
       result: IssueValidationResult;
       projectPath: string;
+      /** Model used for validation (opus, sonnet, haiku) */
+      model: AgentModel;
     }
   | {
       type: 'issue_validation_error';