fix: migrate Qwen Code CLI from TOML to Markdown format (#1589) (#1730)

* fix: migrate Qwen Code CLI from TOML to Markdown format (#1589)

Qwen Code CLI v0.10.0 deprecated TOML format and fully switched to
Markdown as the core format for configuration and interaction files.

- Update create-release-packages.sh: generate .md files with $ARGUMENTS
  instead of .toml files with {{args}} for qwen agent
- Update create-release-packages.ps1: same change for PowerShell script
- Update AGENTS.md: reflect Qwen's new Markdown format in docs and
  remove Qwen from TOML format section
- Update tests/test_ai_skills.py: add commands_dir_qwen fixture and
  tests covering Markdown-format skills installation for Qwen

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: update CommandRegistrar qwen config to Markdown format

extensions.py CommandRegistrar.AGENT_CONFIGS['qwen'] was still set to
TOML format, causing `specify extension` to write .toml files into
.qwen/commands, conflicting with Qwen Code CLI v0.10.0+ expectations.

- Change qwen format from toml to markdown
- Change qwen args from {{args}} to $ARGUMENTS
- Change qwen extension from .toml to .md
- Add test to assert qwen config is Markdown format

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>