feat: Add Qwen Code support

[rlam3]

Summary

This PR adds support for Qwen Code, Alibaba's AI coding assistant. Users can now convert Claude Code plugins to Qwen Code extension format.

Changes

New Files

• src/types/qwen.ts - Type definitions for Qwen extension format
• src/converters/claude-to-qwen.ts - Converter from Claude to Qwen format
• src/targets/qwen.ts - Writer for Qwen extension structure

Modified Files

• src/targets/index.ts - Register Qwen target handler
• src/commands/install.ts - Add --to qwen and --qwen-home options
• README.md - Document Qwen installation

Features

• Agent conversion: Claude agents → Qwen YAML agents with frontmatter
• Command conversion: Supports nested commands with colon separator (workflows:plan → commands/workflows/plan.md)
• Skill preservation: SKILL.md format is compatible, copied as-is
• MCP server config: Converts to qwen-extension.json with variable substitution support
• Settings extraction: Automatically extracts environment variable placeholders as settings
• Context file: Generates QWEN.md with plugin documentation index

Usage

# Convert to Qwen Code format
bunx @every-env/compound-plugin install compound-engineering --to qwen

# Output: ~/.qwen/extensions/compound-engineering/

Output Structure

~/.qwen/extensions/compound-engineering/
├── qwen-extension.json    # Config with MCP servers, settings
├── QWEN.md               # Context/documentation file
├── agents/               # Agent files (.yaml)
├── commands/             # Command files (.md)
└── skills/               # Skill directories (SKILL.md)

Testing

Tested with the compound-engineering plugin:

• ✅ All 35+ agents converted successfully
• ✅ All commands converted (including nested workflows:*)
• ✅ All skills preserved
• ✅ MCP servers converted with appropriate warnings for remote servers
• ✅ Context file generated with full plugin index

Notes

• Remote MCP servers are converted with a warning (Qwen has limited remote MCP support)
• Model aliases are normalized to Qwen-compatible format
• Path references are rewritten from .claude/ to .qwen/