docs: document cert chain flags (--format, --chain-out, --fullchain-out)

[krakenhavoc]

Documentation gaps addressed

Scanned PR #7 (week of 2026-04-27): feat: add full certificate chain download and display support.

New docs added

cert issue flags table — Added two new flags:

• --chain-out (default ./<domain>.chain.pem) — writes intermediate CA chain
• --fullchain-out (default ./<domain>.fullchain.pem) — writes leaf + intermediates

cert submit flags table — Same two flags added (mirrors cert issue).

cert download flags table — Added:

• --format flag with values cert (leaf only, default), chain (intermediates only), fullchain (leaf + intermediates)

cert show — Updated description to note it displays intermediate chain details.

New "Certificate chain" section — Explains the three output files from cert issue/cert submit and the --format values for cert download, with copy-paste examples for each format. Notes that most web servers (nginx, Caddy, HAProxy) expect the full chain.

CI/CD examples — Updated to include --fullchain-out in the cert issue example, which is the typical production usage.

Suggested version bump

PR #7 adds new flags without breaking existing ones. The current release is v0.1.x. Suggest bumping to v0.2.0 (minor feature addition) once PR #7 merges.

Related PRs

• feat: add full certificate chain download and display support #7 — chain download and display (open, pending merge)
• feat: add full certificate chain support app#79 — backend GET /certs/tls/:id/chain endpoint (dependency)
• feat: add chain and fullchain certificate file support cert-action#7 — GitHub Action chain support (companion)

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