Add JSON output format for CI integration

[TheStack-ai]

Context

zclean outputs human-readable text. For CI pipelines or monitoring, a --json flag that outputs structured data would be useful.

What to do

Add --json flag. Output should include:

{
  "found": 5,
  "killed": 5,
  "processes": [{"pid": 1234, "name": "node", "memory_mb": 512}],
  "freed_mb": 2048
}

Files to modify

• src/reporter.js (add JSON format)
• CLI entry point (add flag)

Difficulty: Easy