[process-manager PM-8] Dev loop + ShutdownManager integration (engine side of pm dev)

[rickylabs]

Summary

The foreground dev loop (engine side of netscript pm dev): ShutdownManager integration, ordered teardown, Windows signal caveat (denoland/deno#28081 — listener suppresses default action; re-invoke exit/teardown explicitly).

Scope

• Archetype / area: packages/plugin-process-manager-core engine
• Part of Epic: NetScript Process Manager — bare-metal supervisor + admin console (pup/pm2 done right) #510
• Depends on: [process-manager PM-6] Supervisor loop + composable start policies (autostart/cron/watch) #517 · Blocks: PM-27

Design source

• research/design/d1-supervision-engine-core.md (D1-S9) · plan.md §4 PM-8, R5

Acceptance criteria

• gate: Ctrl+C teardown kills the whole graph in dependency order on POSIX and Windows code paths
• gate: Windows 6-signal caveat handled and tested (explicit exit re-invocation)
• gate: scoped check/lint/fmt wrappers green (--ext ts,tsx)

Non-scope

• CLI UX/multiplexed output rendering (PM-27).

Drift / Debt

• none