Add Qwen TUI integration

[orangewk]

What changed

• add a manifest-driven qwen agent type with interactive qwen -i spawning
• add Qwen turn delivery through a Stop hook
• bridge native Windows hooks through PowerShell, Node, and an explicit Git Bash executable
• install the agmsg skill for existing Qwen Code users
• document standalone Qwen TUI use and Claude Desktop-coordinated workflows
• add registry, join, delivery, syntax, and spawn coverage

Why

Qwen Code can be useful as a bounded TUI worker in an agmsg team, but agmsg had no registered Qwen type, installer target, delivery hook, or onboarding path. On Windows, Qwen's PowerShell hook also cannot directly execute the POSIX agmsg scripts.

The Windows bridge converts Git Bash paths to native mixed paths before PowerShell invokes Node. This avoids the observed /c/... to C:/c/... double conversion.

Validation

• tests/test_qwen.bats: 6/6 passed under native Git Bash
• tests/test_type_registry.bats: 17/17 passed
• isolated installer smoke test passed with an existing .qwen directory
• model-free Windows hook E2E received HOOK-QWEN-OK and returned decision: block
• git diff --check passed

Pending before ready review

The real Claude Desktop -> Qwen TUI -> Claude Desktop model E2E is deferred until the Qwen Token Plan quota resets at 2026-08-06 04:31 UTC (13:31 JST). It will be retried once after reset.

Closes #41