v0.5.0

Added

• --json CLI flag: emits a machine-readable audit report to stdout
  (schema v1) with per-rule results, while logs go to stderr. Designed for
  CI pipelines and automated tooling.
• RuleResult.rule_id: results now carry the stable identifier of the rule
  that produced them (stamped by the auditor), plus RuleResult.to_dict()
  for serialization.
• MCPAuditor.get_audit_report(): returns the full audit
  (score, max_score, summary, per-rule results) as a dictionary.

Changed

• The CLI now uses argparse: mcpscore --help works, and usage errors keep
  exit code 1 (exit code 2 remains reserved for connection failures).
• get_audit_summary()'s by_severity breakdown is keyed by severity name
  (CRITICAL, HIGH, MEDIUM, LOW) instead of numeric value, matching
  its documented behavior.
• CLI logging is explicitly directed to stderr, keeping stdout clean for
  --json output.