Launcher fail-stop: remaining items after #65 (Windows process trees, WSL exit codes, cp932, UNKNOWN escalation, stop races) #66

Remaining items from #64 after #65 (#65 is limited to propagating failures to the Launcher and keeping normal completion compatible, agreed with @tmori):

• Windows: child processes survive a stop. hako_asset_runner.py (~291, ~330) returns early when the parent has already exited, so taskkill /T never runs. Since an exit-0 finish now ends TERMINATED with no failure_report, the leftover children are invisible. Kill the process tree even when the parent is gone (for example a Job Object, or recording child PIDs), and report survivors.
• WSL: Windows .exe assets always report exit_code=None (hako_asset_runner.py ~394). Under the normal-completion rule (hako_launcher.py ~352) every normal finish of such an asset becomes FAILED.
• Non-UTF-8 hako-cmd check output (cp932 on Windows). text=True (hako_cli.py ~118) raises UnicodeDecodeError, which reaches the watch loop and fail-stops with watch_exception. Decode with errors="replace" and treat the result as UNKNOWN.
• A slow version probe disables supervision silently. The 1.0 s probe timeout is cached as "unsupported" for the whole session (hako_cli.py ~212-236). Retry it, or treat a timeout as unknown rather than unsupported.
• Repeated UNKNOWN never escalates. Add a consecutive-UNKNOWN counter (and the last reason) to the session payload, and consider a configurable escalation threshold.
• Stale health result in asset-exit reports. _fail_stop merges _last_health_report into the top level (hako_launcher.py ~199), so an unexpected_asset_exit report can show status: "OK".
• Stop-time races. A user terminate can still end FAILED: an in-flight check returns ABORT, or a killed asset is reported as unexpected_asset_exit, because _stop_watch and TERMINATING are not checked. Live terminate returns ok: true even when the session ends FAILED (hako_launcher_control.py ~467).
• activate() can be left in ACTIVATING when the startup check or _prepare_runtime raises.
• A real-process test of the business-pack flow: a real child exits 0, then the background session reports TERMINATED and hako_launcher_ctl status returns ok.

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