feat(plugins): Process Pack — OS-process introspection (list + info)

[rrader26]

Summary

• New `createProcessPlugin()` adds 2 read-only OS-process tools.
• Cross-platform pure-Node (shells out to `ps` / PowerShell `Get-Process`).
• Read-only in v0; kill / signal sending ships in a follow-up with explicit gating.

Tools

Tool	Use
`agentmark_process_list`	List all running processes; optional name_filter + sort (cpu / memory / name / pid)
`agentmark_process_info`	Per-PID detail: ppid, vsz_kb, memory_kb, state, command line

Why

Read-only OS observability for the agent. Use cases:

• "Is my bridge still alive?" → `process_list` with name_filter
• "What's eating CPU on this box?" → `process_list` sorted by cpu, top 10
• "What spawned this orphan process?" → `process_info` with the PID → look at ppid
• "Why isn't Excel responding?" → `process_info`, check state column

This is also a precursor to the planned Frida-style "enterprise introspection" tier — that work needs a baseline OS-level observability surface to anchor against.

What's NOT in v0

• process_kill — too easy to misuse. Lands in a follow-up with `allow_kill: true` plugin gate + signal whitelist.
• process_open_files (lsof) — `lsof` isn't installed everywhere; need to either declare it required or implement on platforms with native APIs.
• process_network (netstat / ss) — same issue.

Test plan

• `pnpm build` clean
• `pnpm test` — 354 pass / 10 skip (12 new tests against live `ps`, no mocks)
• Manual on Windows VM: `agentmark_process_list { name_filter: "node" }` returns the agentmark MCP server itself

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