fix: Use FatalErrorRespectJSON across all commands (bd-28sq)
Convert all fmt.Fprintf(os.Stderr, ...) + os.Exit(1) patterns to use
FatalErrorRespectJSON for consistent JSON error output:
- dep.go: dependency commands (add, remove, tree, cycles)
- label.go: label commands (add, remove, list, list-all)
- comments.go: comment commands (list, add)
- epic.go: epic commands (status, close-eligible)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
efdaa93789