feat: add du/df/ps output filter

[bug-ops]

Parent: #717

Problem

du -sh * can be long. ps aux lists all processes. df -h is usually fine but du can be huge.

Acceptance Criteria

• Match du, df, ps
• du: sort by size descending, keep top-20, summarize rest
• ps: group by command name, show top-10 by CPU/mem
• df: pass through (usually short)
• Config: [tools.filters.system] with enabled flag
• Tests
• Expected savings: 60-85%