fix(frontend): align issue types with backend enums

- Fix IssueStatus: remove 'done', keep 'closed'
- Add IssuePriority 'critical' level
- Add IssueType enum (epic, story, task, bug)
- Update constants, hooks, and mocks to match
- Fix StatusWorkflow component icons

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

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

frontend/src/features/issues/components/StatusWorkflow.tsx

@@ -26,7 +26,6 @@ const STATUS_ICONS = {
   in_progress: PlayCircle,
   in_review: Clock,
   blocked: AlertCircle,
-  done: CheckCircle2,
   closed: XCircle,
 } as const;