v0.16.1

A focused fix for the silent invite: in solo mode or while autoplay is running,
invite_ai_teammate and continue_ai_teammate would sit at pending forever — no teammate
window, no log, dual_launch_outcome stuck at Idle. These refusals are now recorded as
Rejected with a readable reason and the call answers 409 pointing at the cause. Verified the
failing behavior and the fix in the same isolated game session (offline suite: 866 C# tests,
423 Python tests, all gates).

• 邀请队友失败现在有明确原因。 在单人模式或自动游玩进行中调用 invite_ai_teammate/continue_ai_teammate，以前会一直挂在 pending：双开任务在第一道模式门就被无声拒绝，既不写状态也不写日志，dual_launch_outcome 永远停在 Idle。现在这类"玩家可修复"的前置失败会记录为 Rejected 并附可读的告知文本（切到多人模式 / 先暂停自动游玩），请求返回 409 指向原因；真正并发在途的尝试语义不变，仍是 pending。该缺陷在 --force-steam off 的隔离档实机中复现（邀请 8 分钟无任何反馈），已加离线回归。

Validation

• Fix reproduced and verified in an isolated game session: before the fix, invites hung at pending for 8+ minutes with no feedback; after the fix, invite answers 409 invite_failed with the mode explanation and /health shows dual_launch_outcome=Rejected.
• Offline: 866 C# tests, 423 Python tests, all verification gates, CI on PR #200.
• Real Steam profile untouched.

Build

• Source commit a64e052710fa08a74b54418a78af6bd17d54b2fc (clean tree)
• sts2-ai-agent-v0.16.1-windows.zip: 779153 bytes, SHA256 835E22E871DD4A217766F5E02043312D2B144E9D81CEB00B75B32B49D37C7551