feat(pm): Windows Task Scheduler adapter — cron-policy processes compile to Scheduled Tasks [PM-C]

[rickylabs]

Part of #510.

A third OS backend beside systemd/Servy: Windows Scheduled Tasks for PM processes whose start
policy is cron — periodic/triggered workloads register with the OS scheduler instead of running
as resident services (no idle footprint on consumer/prosumer machines; survives reboot; OS owns
the trigger).

Fits the ratified PM architecture with no new concepts:

• PM-19 compile mapping: autostart/watch policy → Servy service (shipped adapter); cron
  policy → Scheduled Task (new renderer + adapter, schtasks.exe-backed).
• PM-17 capability descriptor: the task backend advertises {triggers, runAs, non-resident};
  warn-and-omit for knobs it can't honor (e.g. WatchdogSec-class).
• PM-18 seam: the windows target's ServiceDeployTargetPorts grows the task sibling.

Upstream trajectory (wrap, don't block): denoland/deno#33965 scaffolds Deno.cron.persistent
(register with crontab/launchd/schtasks; CF-Workers-style default.scheduled worker entry) —
currently API-only, all backends "not yet supported", behind --unstable-cron; per-OS backends
land in follow-up PRs. v1 wraps schtasks.exe directly (the Servy doctrine); when upstream
backends ship, adopt Deno.cron.persistent as the first-party registration path and align the
worker-entry shape.

• gate: render + register/unregister round-trip against real schtasks (Windows runner)
• gate: capability descriptor accurate; warn-and-omit tested; PM-19 compile mapping test
• gate: reboot survival — task fires after restart without any resident NetScript process

Depends on: PM-17 #528, PM-19 #530. Design source: PR #822 (rfc.md) + run .llm/runs/rfc-single-deployment--orchestrator/.