feat: add list health check flags

[steipete]

Summary

• Extend mcporter list with --status, --exit-code, and --quiet instead of adding a separate health command.
• Keep status checks on the existing list discovery/classification path, including JSON counts and per-server issue envelopes.
• Document the new flags in README, quickstart, CLI reference, and changelog.

Proof

• ./runner pnpm check
• ./runner pnpm test
• ./runner pnpm exec vitest run tests/cli-list-flags.test.ts tests/cli-list-json.test.ts tests/cli-list-classification.test.ts tests/cli-list-formatting.test.ts tests/cli-list-stdio-logs.test.ts
• Live CLI: failing stdio server with list bad --status --json --exit-code returns exit 1, emits parseable JSON, and keeps captured stderr out of stdout.
• Live CLI: failing stdio server with list bad --quiet returns exit 1 and emits no stdout.
• Codex autoreview: clean after fixing the accepted selector-validation finding.

Replaces

• Supersedes feat(health): add mcporter health for at-a-glance server status #176 by folding the health/status concept into the existing list command surface.