fix: address PR review comments for GitHub issue comments feature

- Use GraphQL variables instead of string interpolation for safety
- Add cursor validation to prevent potential GraphQL injection
- Add 30s timeout for spawned gh process to prevent hanging
- Export ValidationComment and ValidationLinkedPR from validation-schema
- Remove duplicate interface definitions from validate-issue.ts
- Use ISO date format instead of locale-dependent toLocaleDateString()
- Reset error state when issue is deselected in useIssueComments hook

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/ui/src/components/views/github-issues-view/hooks/use-issue-comments.ts

@@ -101,6 +101,7 @@ export function useIssueComments(issueNumber: number | null): UseIssueCommentsRe
       setHasNextPage(false);
       setEndCursor(undefined);
       setLoading(false);
+      setError(null);
     }
 
     return () => {