Feature: machine-readable output (--json)

[korya]

Problem

Output is human-formatted prose on stderr only. There is no structured form, so a CI job or monitoring agent that wants to know which assertion failed has to scrape:

Error: Cannot perform request: 4 assertions failed:
- ok: expected OK, got 500 ("500 Internal Server Error")
- status: expected 200, got 500 ("500 Internal Server Error")
- header[X-Nope]: expected "1", missing
- body: expected "zzz", got "boom"

Proposed

--json   Emit a machine-readable result document on stdout

Roughly:

{
  "url": "http://…/500",
  "method": "GET",
  "status": 500,
  "duration_ms": 0.51,
  "passed": false,
  "assertions": [
    {"kind": "ok",     "passed": false, "expected": "2xx-3xx", "actual": 500},
    {"kind": "status", "passed": false, "expected": 200,       "actual": 500}
  ]
}

Why it matters

Enables dashboards, alert payloads, and JUnit-style conversion for CI reporting. Pairs naturally with the stdout/stderr split requested separately.