feat: Add Unix-friendly issue index with multiple output formats

- Add issue-index command with TSV, CSV, JSON, and fields output formats
- Support sorting by number, title, priority, state, created, updated
- Add filtering by state (open/closed) and priority level
- Include proper data cleaning for Unix pipeline processing
- Add make targets: issues-get, issues-csv, issues-json, issues-high
- Optimize for awk, cut, grep, and other Unix text processing tools

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

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

.gitignore

@@ -89,3 +89,4 @@ debug_*.py
 # Claude Code local settings (user-specific permissions)
 .claude/settings.local.json
 
+.aider*